An archive containing a piece of software (be that in binary or source form) as well as MetaData about that software. This is at least a human readable description of the packaged software. In nearly all [Package] formats it also extends to a list of architectures the particular [Package] will run on, and a list of other [Package]s are required in order for the software in this one to run correctly. These are called dependencies. Many [Package] formats also have provisions for storing a maintainer contact, a checksum and/or a cryptographic signature of the [Package], its license, and more. Together, these pieces enable the PackageManagementTool to fulfill its PackageManagement duties.
The two most common formats are [RPM] (invented by RedHat and used by most [LinuxDistribution]s) and [Deb] (designed for [Debian]; obviously also used by [Debian]-derived [LinuxDistribution]s).
[Slackware] has the simplest [Package] format: almost plain [TarBall]s of the installed software, the MetaData simply consisting of a file with a description of the package and a postinstall script. There is no information about dependencies. This is not necessarily a drawback; on simple setups (such as many dedicated servers use), the fact that no (corruptible) DataBase of installed [Package]s needs maintaining can be desirable.
Upcoming