What does "-45.el7" mean in "httpd 2.4.6-45.el7"? I have installed `httpd` on CentOS 7, but the installed version is `2.4.6-45.el7`. This page says that the latest version of `httpd` is 2.4.25. I want to know if `2.4.6-45.el7` is equivalent to `2.4.25`. What does `-45.el7` mean? Is there any documentation about this?

That's version 2.4.6 and the part after the `-` is the package release version.

`el` (no `e1` as stated in the question) represents `Enterprise Linux` and the following is its corresponding version (`7`). This version is consistent across RedHat and related distributions (including CentOS).

The packaging version changes when it has to be rebuilt because of a change to another package, which is why it increases even though the actual source package is still the same.