Search engine optimization, in short SEO, refers to all measures aimed at improving the positioning of individual web documents in SERPs. Search engine optimization is a field of search engine marketing (SEM). Contrasting to this is the negative SEO.
The term Search Engine Optimization (SEO) refers to all technical and content-related measures on websites that are implemented with the intention of improving rankings in the SERPs. Search engine optimization is a sub-area of search engine marketing (SEM) and thus online marketing. Today, the abbreviation SEO is also translated as Search Experience Optimization, as improvement in usability is also becoming part of SEO as the focus of optimization measures is on users and search engines.
The search within the WWW is becoming more and more important with the growing amount of information on the Internet. For example, many websites today would not be found on the internet if there were no search engines. The past decade saw many search engines come onto the market. Prominent examples include Bing, Baidu, Yandex, and of course, Google by Google Inc. Google has managed to position itself as the market leader. The search engine giant from California has become dominant particularly through its unique features which include simplicity, speed, and high relevance. In addition to a powerful crawler, Google uses a complex algorithm to review the crawled pages and present these within the relevant context in the search results. This algorithm is constantly enhanced to optimally adapt the search results to searchers and their needs. When optimizing for Google, there are numerous factors that should be given special attention. Analogous to the emergence and further development of web search engines and the increasing importance of the Internet, the discipline of "search engine optimization" has developed as a sub-area of online marketing.
When the first commercial websites were launched on the internet in the mid-1990s, professional search engine optimization was established parallel to this. However, the measures used at the beginning of the internet age are hardly comparable with SEO today. At that time, search engines were still heavily reliant on meta elements to determine the quality of a website, and they used this data to determine the ranking. In addition, in the early day of the internet, a website had to be registered with search engines in order to be indexed.
When search engine optimization was first established, it usually involved the keyword optimization of meta-data, text elements on the website, and generating as many backlinks as possible. The rule for optimizing keywords was relatively simple: the more the desired keyword appeared on the website in meta-data and texts, the greater the visibility of a website in the search results lists. At that time, the meta keywords were used by SEOs as well as search engines to establish relevance. As far as the link structure is concerned, it was also relatively easy to achieve success. It was simply the masses that counted. When Google introduced the Page Rank (PR) in 2000, it was also important to have the highest possible level of PR when linking.
Search engines were therefore very susceptible to manipulation, as keyword stuffing alone could achieve great ranking successes. As a result, Google tightened their quality guidelines, because in many cases, the websites that dominated the search results lists were not the best websites, but the most manipulated.
The history and development of search engine optimization can be read on Google Updates. In 2003, for example, Google took a more targeted approach to combating hidden content with its updates "Cassandra" and "Florida". Spam measures such as keyword stuffing with white text on a white background no longer worked. In the same year, Google introduced another algorithm change to make mass linking from link farms more difficult. Thanks to the brandy update, SEO became more focused on thematic relevance than on pure keyword density. Technical aspects also became more important. Google therefore launched Google Webmaster Tools in 2004, today Google Search Console. For example, webmasters can upload a XML Sitemap so that Google can index the website better.
Until 2005, SEOs were still relatively free in their link structure and did not have to fear any sanctions. However, this changed with the Allegra update from Google. Since this update, websites can be penalized for manipulative measures by ranking losses or exclusion from the Google index. Duplicate content has also become an increasing problem. Until now, many SEOs had relied on content that was distributed several times on their own website to increase relevance. In the mid-2000s, the Universal Search also became increasingly important. That's why SEOs focussed on pictures or videos whilst optimizing, since they could now be displayed as vertical search results in the Google SERPs. In these years, Google continuously developed its algorithms. The meta keywords and the Meta Description no longer had any relevance to the ranking. It had also become almost impossible to achieve good rankings with massive link building via Satellite Pages or link directories.
A real SEO paradigm shift could be seen after the introduction of the two major Google updates "Panda" and "Penguin". They are both jointly responsible for ensuring that Google can better determine the quality of a website. In addition to technology, the content of a website has thus become much more important for search engine optimization. In this context, the formula TF*IDF for the term weighting of a website was also discovered. It has replaced Keyword Density as a KPI.
Modern search engine optimization has to take many different aspects into account. In April 2015, for example, Google's mobile device friendliness was ranked as a ranking factor. Since then, it has become important to integrate Mobile Optimization into an SEO strategy to avoid ranking losses in the mobile search. Likewise,Technical SEO plays a very important role today, since loading times or bounce rates can influence the rating of a website. In addition, https encryption of websites has become a ranking factor. All in all, it can be assumed that user signals are becoming increasingly important for search engine optimization. Therefore, many people no longer talk about Search Engine Optimization (SEO) but about Search Experience Optimization (SXO). 
As an online marketing channel, SEO is one of the most important disciplines and should not be neglected in the overall online marketing mix. Search engine optimization is a permanent optimization process that often takes a long time before the results can be visible. The actual optimization is done on the pages and is referred to as OnPage optimization. The popularity of the page can be improved through OffPage optimization. These two measures are described in detail below.
OnPage optimization deals with all measures on a web document itself. This focuses on the technical and content optimization of a page. Factors such as page architecture, internal linking, text, and metadata are essential for the evaluation of the relevance of a page by search engines. The usual approach in the optimization is the creation of a landing page for a special keyword (also referred to as search term) that is displayed in the search results pages (SERPs) when this term is searched. In the web document, important factors such as the placement of relevant content (text, images, and videos), metadata, and internal links are set in a manner that is compliant with the search engine. This also simplifies the crawling and inclusion of the page in the search engine index. The optimization of content can be done on the basis of a keyword, but should be "holistic", meaning that a topic should be dealt with as comprehensively as possible so that all possible user needs can be satisfied.
Further subdivisions of the OnPage optimization:
As opposed to OnPage optimization, OffPage optimization deals with the popularity of a page on the Web. Basically, this comes down to the reputation of a page based on the number and quality of external links (also called backlinks). These are links from other websites that point to a web document. OffPage optimization is a large part of search engine optimization and is usually a greater challenge for webmasters since one cannot directly influence the links from other pages. The Google algorithm also places emphasis in this area on certain ranking factors such as link popularity, trust or the position of a backlink on the other pages. According to Google, there are over 200 OffPage factors that can influence the ranking.
In order to make the success of search engine optimization measurable and scalable, certain tools that help analyze the success of the optimization are required. There are several SEO analysis tools on the German market, some of which are available free of charge. The most common include Searchmetrics, Ryte, Sistrix Toolbox, Advanced Web Ranking, and Strucr. These tools can be used for both OnPage and OffPage analysis. In addition, webmasters should also use web analytics tools such as Google Analytics to monitor and analyze user traffic. Such tools help monitor one’s own ranking as well as determine appropriate optimization measures.
For a long time, search engine optimization was not been taken seriously as a partial discipline of marketing. However, with the increasing professionalization of the scene, which continues to advance with its own exhibitions, conferences and numerous literature, search engine optimization has become a firmly established part of online marketing. At the same time, the individual sub-areas have continued to develop, so that today there are often no longer SEO generalists, but specialists for specific topics such as local SEO or technical SEO. At the same time, search engine optimization has also found its way into many subjects of study, meaning that the scientific occupation with the subject "SEO" is also being continuously expanded.