Star clusters are just that - a cluster of stars. The stars all belong to our Milky Way galaxy, but are bound to one another by gravity.
"Open clusters" are where the stars are spread out significantly, but are still bound together. "Globular clusters" are tightly-bound "balls" consisting of hundreds of thousands of stars.
Open clusters are very beautiful targets for binoculars because they are typically spread out and often display various star colors. Some clusters are accompanied by dust ,called nebulosity, that glows due to the light of the stars. A famous example is The Pleiades with its blue nebula.
© Barry Etter, Mocksville, NC