Many stars occur in associations called "star clusters".
Astronomers divide star clusters into two broad categories: Open Clusters (also called Galactic Clusters), in which there are a few (typically tens to thousands of) young stars that formed together and are loosely bound by gravity and individual stars are easily resolved. The other category is the Globular Clusters. Globular Clusters are huge, dense spherical balls containing many more stars (typically 100,000 to 1,000,000), grouped together in a region 300 or so light years in diameter. Globular clusters are very old, having existed since soon after the galaxy was formed approximately ten billion years ago. and in which the central density is sufficiently high that we can not resolve individual stars from earth-based telescopes. The Pleiades in the constellation Taurus are the most famous example. Globular clusters can be observed with the naked eye, or binoculars, and look like hazy mothballs. When observed through a telescope, hundreds of the myriad stars which make up the globular cluster can be observed.
The following images show examples of these two types.

The Pleiades Star Cluster. Picture Credit: Mount Wilson Observatory. The Pleiades star cluster, M45, is one of the brightest star clusters visible in the northern hemisphere. It consists of many bright, hot stars that were all formed at the same time within a large cloud of interstellar dust and gas. The blue haze that accompanies them is due to very fine dust which still remains and preferentially reflects the blue light from the stars.

Globular Cluster M5. Credit: Anglo-Australian Telescope Photograph by David Malin Copyright: Anglo-Australian Telescope Board The globular cluster M5, pictured on the left, contains roughly 100,000 stars. These stars formed together and are gravitationally bound. Stars orbit the center of the cluster, and the cluster orbits the center of our Galaxy. So far, about 160 globular clusters are known to exist in a roughly spherical halo around the Galactic center. Globular clusters do not appear spherically distributed as viewed from the Earth, and this fact was a key point in the determination that our Sun is not at the center of our Galaxy. Globular clusters are very old. There is a straightforward method of determining their age, and this provides a very interesting lower limit on the age of our universe of about 14 billion years