In OS X, what's the difference between a package and a metapackage?

Question

The .mpkg and .pkg extensions seem to be the only difference. Surely there's more to it than that?

Answer 1

.pkg files are just regular installers. I've read that with .mpkg the your able to select and deselect other .pkg files.

Answer 2

These packages do not contain actual software, they simply depend on other packages to be installed. This setup allows entire sets of software to be installed by selecting only the appropriate metapackage. For example, an Ubuntu user can install the Kubuntu environment (KDE and all its associated programs) by selecting "kubuntu-desktop."