The term used in Debian Policy for the main, contrib, and non-free divisions.
The type of system a piece of software is built for.
Such as amd64, i386, armel, s390x, powerpc, armhf, mips, AArch64, POWER.
An installable .deb file
A unit of upstream software (with a single build system)
A repository holding one particular "branch" of Debian's development process.
Such as unstable, testing, stable, oldstable.