From [http://www.backports.org www.backports.org]:

You are running Debian stable, because you prefer the stable Debian tree. It runs great, there is just one problem: the software is a little bit outdated compared to other distributions. That is where backports come in.

Backports are recompiled packages from testing (mostly) and unstable (in a few cases only, e.g. security updates), so they will run without new libraries (wherever it is possible) on a stable Debian distribution. It is recommended to pick out single backports which fits your needs, and not to use all backports available.