From Seo Wiki - Search Engine Optimization and Programming Languages
S4J stands for Software For Joomla, or Software4Joomla. Another word for software would be extensions. Example: s4jMostVisited is an extension or a plugin, written in PHP that can be used to expand on a functionality when using Mambo or Joomla! Content Management Systems (CMS) combined with the Community builder. It allows the webmasters to build a feature-rich website without website programming knowdledge. In case of s4jMostVisited, this would allow the webmaster to enable a feature that shows website visitors which Community Builder (CB) Profile has been visited most often.
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