Original: Two types of star clusters can be distinguished : globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound , while open clusters , a more loosely clustered group of stars , generally contain less than a few hundred members , and are often very young .
Simplified: Globular clusters are tight groups of hundreds and thousands of very old stars . Open clusters are more loose , and they have less than a few hundred stars , which are often very young .