1. Principally US: One or more sets, usually in the context of gambling . See also ahead race (a.k.a. ahead session ) for a more specialized usage.
2. Principally British: Any of a group of pre-determined frames played in a match too long to be completed within a single day's play. A best of 19 frame match , for example, is generally played with two "sessions", the first composed of nine frames, the second of ten. This term is generally used only in the context of professional snooker , as matches at the amateur level are rarely played over more than nine frames. Longer matches can be split into three or four sessions.