Apache is an HTTP server that has a large installation base within the UNIX & Linux community.
The server has already gone through several iterations, resulting in similar but not 100% compatible installations and configurations. Make sure to include the particular version number of the Apache version used, in the question.
Apache 2.4 ships with modern distros (state: 2014-10), but older versions (2.2, 2.0 are often included as well for compatibility reasons). Extensions (e.g. 'mod_wsgi`) are available as separately installable packages.