Binary Stars is a system in which 2 stars are bound together by gravity, The brighter star is the primary star, while the dimmer is the secondary.
Open Clusters is a group of up to a few thousand stars that were formed from the same giant molecular cloud, and are still loosely gravitationally bound to each other, it contains thousands of stars.
Globular Clusters is a tightly clumped spherical groups of millions of stars. It is a large group of old stars that are closely packed in a symmetrical, somewhat spherical form.
