A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting in a stable, compact formation.
Globular clusters are found in nearly all galaxies. In spiral galaxies like the Milky Way, they are mostly found in the outer spheroidal part of the galaxy – the galactic halo. They are the largest and most massive type of star cluster, tending to be older, denser, and composed of lower abundances of heavy elements than open clusters, which are generally found in the disks of spiral galaxies. The Milky Way has more than 150 known globulars, and there may be many more.
Both the origin of globular clusters and their role in galactic evolution are unclear. Some are among the oldest objects in their galaxies and even the universe, constraining estimates of the universe's age. Star clusters were formerly thought to consist of stars that all formed at the same time from one star-forming nebula, but nearly all globular clusters contain stars that formed at different times, or that have differing compositions. Some clusters may have had multiple episodes of star formation, and some may be remnants of smaller galaxies captured by larger galaxies.
REF: Wikipedia
Rho Ophiuchi Nebula
Sculptor Galaxy and NGC-288
Messier 13
Messier 14
Messier 15
Messier 10
Messier 05
NGC 5139
Messier 03
NGC 5466
NGC 2419
Messier 54
Messier 80
Messier 92
Messier 22
NGC 5053
Messier 53
Messier 12
Messier 09
Messier 04