Jam sessions occur when any group of musicians spontaneously gather to informally play or sing together. Members of different ensembles who do not normally play with each other, can play together just for the sake of making music. Spontaneous improvisation is one of the key factors of a jam session and can often be used as part of a song-writing process. Jamming can be a literal term – because people often have to "jam" themselves into confined spaces given the number of people involved – e.g. in the case of jazz four or five ensembles might get together at a time.