A BGP route can be associated with one or more communities. There are three kinds of BGP communities:
standard communities (each 4 bytes in length, all packed into a path attribute with type code 8)
extended communities (each 8 bytes in length, potentially many possible subtypes, all packed into a path attribute with type code 16)
large communities (each 12 bytes in length, all packet into a path attribute with type code 32)