恒星集团或恒星云是恒星的集团，可以区分为两种类型：球状星团是由成千上万颗老年恒星被万有引力紧密束缚在一起的恒星集团；而疏散星团一般只有数百颗恒星，而且通常都很年轻的恒星组成，是结构较为松散的恒星集团。疏散星团在银河系中运动时会受到巨大分子云的影响，而随着时间的流易逐渐瓦解，但星团中的成员即使不再受彼此间的引力约束，但仍将继续维持大致相同的运动方向在空间中移动；然后他们会被称为星协或是移动星群。

肉眼可见的恒星集团包括昴宿星团、毕宿星团和蜂巢星团。

Star clusters or star clouds are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds or thousands of very old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain fewer than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a stellar association, sometimes also referred to as a moving group.