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.
散開星団 (open cluster) is a gravitationally bound group of stars, while 運動星団 (moving cluster) is defined by shared motion rather than gravitational binding.
星団 (star cluster) is a general term; 運動星団 is a specific type characterized by common proper motion.
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'.