"Apache" is the name of a foundation that write open-source software. Apache HTTPD is a web server written in portable C (when people say "Apache", they usually mean Apache HTTPD.) It mostly serves...
Apache is an open source web server that's supports php, Apache is known to be open source because the source code is available for configuration as per your requirements, its a Linux based product....
You should always use the latest version of Apache (as of October 2009, it is 2.2.14). Older versions may have security flaws or bugs that were fixed in a later release.