What is SSI?
SSI stands for “server-side include,” a type of HTML instruction telling a computer that serves Web pages to dynamically generate data, usually by inserting certain variable contents into a fixed template or boilerplate Web page. Used especially in database searches. In order to use Server Side Includes, your server must be configured to support them.
SSI can help make your pages more responsive and can even help make maintaining your site an easier task. SSI is primarily used to “paste” the contents of one or more files into another. For example, a file (of any type, .html, .txt, etc.) containing a daily quote could be included into multiple SSI-enabled pages throughout a website by placing the following code into the desired pages:
There is no official standard for SSIs, so every Web server is free to support different SSIs in different manners. However, many SSI commands, such as #include and #exec, have become de facto standards.
Server Side Includes
Change one file and every file that uses that include is instantly updated.
Every server language supports them in one form or another.
Easier to reuse code pieces.
Server has to parse each page that uses includes, which can slow down your server and make your site feel slower.