Page "Open cluster" Paragraph 35

After a cluster has become gravitationally unbound, many of its constituent stars will still be moving through space on similar trajectories, in what is known as a stellar association, moving cluster, or moving group.

Several of the brightest stars in the ' Plough ' of Ursa Major are former members of an open cluster which now form such an association, in this case, the Ursa Major moving group.

Eventually their slightly different relative velocities will see them scattered throughout the galaxy.

A larger cluster is then known as a stream, if we discover the similar velocities and ages of otherwise unrelated stars.