The smallest unit that can be managed by Pyrus or the PEAR Installer is a package. A package is a collection of files that are organized and defined by a meta-information file called package.xml.

A package also contains meta-information about the collected files, such as the name of the package, the channel that the package is from, the version of the package, information on the developers who created the package, and any external dependencies the package has on other packages or installation requirements (such as minimum PHP version).

Packages can exist as a collection of files on disk, or can be placed into an archive in phar, tar, or zip format and then later installed on another system.