A copolymer is a polymer made from more than one monomer. There are several type of copolymers named for their configurations. The Different monomers are assigned an arbitrary letter to differentiate them.
Block copolymers are arrangements of several repeats of each monomer, such as AAAABBBBBBAAAAAABBBB. Block copolymers might form based on the interactions of the monomers or they might be made intentionally by slightly polymerizing each monomer separately before mixing them. A random copolymer has no definite pattern. Copolymers are assumed to be random or of unknown configuration unless otherwise specified.