The spherical region of old stars and globular clusters surrounding the Milky Way is the Galactic halo.
More precisely, this description refers to the Milky Way’s stellar halo, a roughly spherical population extending far beyond the flat galactic disk. Its stars are generally very old, metal-poor, and moving in varied, often highly elongated or inclined orbits rather than following the orderly rotation of the disk.
Globular clusters are especially useful markers of the halo. These dense, spherical groups can contain thousands to millions of stars, many formed more than 12 billion years ago. About 90% of the Milky Way’s globular clusters lie within roughly 100,000 light-years of the Galactic Center, although some are much farther out.
“Galactic halo” can also mean the galaxy’s dark-matter halo or its hot gaseous corona, so “stellar halo” is the most technically precise term here. The Galactic bulge is the dense central region, while the disk is the thin, rotating structure containing the Sun and most ongoing star formation.