moving cluster
Astronomical term for a group of stars that share a common motion through space, such as the Ursa Major Moving Group.
The Ursa Major Moving Group is one of the well-known moving clusters.
Compound of 運動 (うんどう, 'motion') and 星団 (せいだん, 'star cluster'), literally 'motion star cluster'. The term is a direct translation of the English 'moving cluster'.