50S is the larger subunit of the 70S ribosome of prokaryotes. It is the site of inhibition for antibiotics such as macrolides, chloramphenicol, clindamycin, and the pleuromutilins. It includes the 5S ribosomal RNA and 23S ribosomal RNA.

Note: Sometimes the '50s is used as shorthand for the 1950s, the 1850s, or other such decades in various centuries – see List of decades