Note: this article name (or a redirect to it) is a homophone with session.
Most broadly, cession (to cede) is the assignment of property to another entity. In international law it commonly refers to land transferred by treaty. Cession is "a surrender; a yielding; a giving up."

Specific areas of law
This is a yielding up, or release. France ceded Louisiana to the United States by the treaty of Paris, of April 30, 1803. Spain made a cession of East and West Florida by the treaty of February 22, 1819. Cessions have been severally made of a part of their territory by New York, Virginia, Massachusetts, Connecticut, South Carolina, North Carolina, and Georgia.