Globular clusters are spherical collections of mostly ancient stars numbering between tens of thousands to a million or more stars stretching 100 to 300 light years across. They are truly ancient structures with a minimum age of about 11 billion years. Most are believed to have formed at the same time as their parent galaxy. To date there are over 160 globular clusters discovered in our Milky Way.
[description from Rob Gendler’s primer]