Perl and Apache are a powerful and popular combination. There are several projects that use these two technologies.
Allows embedding of Perl in HTML pages. These pages are processed in the server before they are delivered to the client. It is similar to PHP. You can learn more here.
The Mason project embeds Perl in HTML with a reusable component model approach. It allows caching, templating, etc.
Mod_perl is one of the most veteran and successful Apache projects. It embeds a Perl interpreter in Apache and allows access to the web server internals from Perl. This allows for entire modules to be written in Perl or a mixture of Perl and C code. In the 1.3 Apache versions, one interpreter has to be embedded in each child, since the server is multiprocess based. In heavy traffic dynamic sites, the increased size could make a difference. Apache 2.0 is multithreaded, as recent versions of Perl are. The next generation of mod_perl takes advantage of this and allows for sharing of code, data and session state among interpreters. This results in a faster, leaner solution.
Make sure you check also Axkit