Raspbian is based on Debian and its repositories share the same code names. Basically:
wheezy-staging are Debian 7 (code name Wheezy)
jessie-staging are Debian 8 (code name Jessie)
stretch-staging are repositories for Debian 9 (code name Stretch)
Repositories for officially released versions contain latest stable release. Repositories with the
-staging suffix contain Debian 7 and 8 backports introduced into staging, but not yet officially released.
Repositories for not yet official Stretch contain latest releases according to their release cycle.
Special names (most likely symbolic links on server side):
Raspbian follows suit.
Each directory contains a
Release text file containing description of the repository and its contents. For example the top of
jessie looks like:
Date: Sat, 24 Dec 2016 22:16:29 UTC
Components: main contrib non-free rpi firmware
Description: Debian armhf testing distribution for Raspberry Pi
12cc500e77458577d74c1b7ca9dc2495 46783235 main/binary-armhf/Packages
3a5b29b8ee151a01bd9937e5ddd6a72f 12472162 main/binary-armhf/Packages.gz