A residence permit is a residence document or title issued under the German Residence Act (§ 7 AufenthG). Citizens from countries outside the EU generally require a permit to enter and stay in Germany. A residence permit is temporary and bound to a specific purpose. These purposes include: training (§§ 16-17 AufenthG), employment (§§ 18, 18a, 20, 21 AufenthG), international law, humanitarian, and political reasons (§§ 22-26, 104a, 104b AufenthG) or family reasons (§§ 27-36 AufenthG). A residence permit is not always associated with a work permit; the latter must be mentioned explictly on the residence permit. It may be extended or converted to a settlement permit. The immigration authorities are responsible for issuing residence permits.

Source: Bundesministerium des Innern, Wikipedia, edited (only available in German)