Freely distributable programs whose source code is freely available for developers to modify.
Open rate is the ratio between opened and unopened emails that are written as part of a direct marketing strategy, so-called direct marketing. In reality, this ratio is usually around 50%.
SEO that takes place outside the website itself. Most of the time it is linkbuilding.
Translated, this is "organic search". The term is used for search results in search engines (Google, Seznam) that are not influenced by PPC (or other) advertising. To get a good position in organic search, SEO techniques are used, which deal with setting the quality of the site sufficient for the user and for the search engine algorithms. Organic search results are also affected by linkbuilding, which is part of SEO (poorly done linkbuilding can also affect results negatively).