Here you can put extended tag descriptions which are shown on post list page when filtering by a tag(s). Simply create a file named ".html" (always in lower case, e.g.: "php.html") and enter the description there (you can use HTML). You can also create descriptions using wiki markup - for this simply create a ".wiki" (or .wacko, or .txt) file. If there are both .html and .wiki files .wiki takes precedence.