A session of a role-playing game is a continuous period of time in which a group gathers at a table (either in person or remotely) to play a specific game together in real time. Although players may take breaks from the game while gathered, a session is generally not considered over until the players go their separate ways or, more rarely, start playing a different game.
Length
A session does not have a fixed duration and may last less than an hour or over a day. Some game systems (particularly systems designed for one-shot games) may have built-in conditions that, once fulfilled, end the game or session. In these cases, sessions of games using those systems are likely to be of similar length to each other. In other cases, sessions usually end by player agreement. For example, the game Microscope is designed to be played for any length of time until players decide to stop.
Sessions in asynchronous play
In asynchronous play (e.g. play-by-post), play might be divided up into "sessions" based on the content of those sessions. For example, a substantial period of play that takes place in a specific location might be referred to as a session, or session breaks might be determined by narratively satisfying pauses in the narrative.