There are two types of star clusters. Globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, are more loosely clustered, generally containing less than a few hundred stars, and are usually very young.
An open star cluster is a smaller group of stars, maybe only a few thousand or so that are loosely held together by gravity as they orbit within a galaxy. A globular cluster contains many more stars, which are usually a lot older. The globular clusters are usually found closer to the centre of a galaxy. Their name come from their spherical cloud shape, like a globe. They are held together more tightly by gravity and can stay intact for much longer than an open star cluster.
There isn't enough information presented here to come up with a reasonable answer.
Much much bigger
It can be called a star cluster, an open cluster or an asterism.
open cluster
globular cluster
The H-R diagram of a star cluster is missing the upper part of the main sequence
similar age and composition.
Constellation or "asterism". The difference is that "constellations" are officially recognized by the International Astronomical Union, while an "asterism" is any other pattern or grouping of stars.
It can be called a star cluster, an open cluster or an asterism.
open cluster
open cluster
open cluster
A star cluster is a cluster of stars, so clearly a star cluster must be larger.
Some of the brightest stars in the open cluster are found in the "Plough" or the "Ursa Major" just like the Epilson Ursai Majoris.
globular cluster
globular cluster
The Pleiades is a open star cluster. It contains mostly blue-white type stars, so the colour of the cluster would appear to be blue-white. However, it is a cluster and not a single star. See related question.
Because of the high percentage of OB stars, the cluster is a relatively young cluster. M26 has an estimated age of only about 25 million years.
star cluster