6.2 What is the format of a Debian binary package?
A Debian "package", or a Debian archive file, contains the executable
files, libraries, and documentation associated with a particular suite of
program or set of related programs. Normally, a Debian archive file has a
filename that ends in .deb.
The internals of this Debian binary packages format are described in the
deb(5) manual page. This internal format is subject to change
(between major releases of Debian GNU/Linux), therefore please always use
dpkg-deb(1) for manipulating .deb files.