Score is a slang term which has numerous definitions. The meaning of the word score depends on the context of the conversation.
Score is sometime used to describe the act of having sex. For example, someone saying "I scored last night," means they had sex last night. This term is mostly used between male individuals.
Settle the score is a term often used by individuals seeking revenge. For example, someone who was robbed might be looking to settle the score with their robber.
Score is also used as a slang to describe the act of killing someone. This term derive from Basketball in which players score by shooting a ball into a basket; when a gangster shoots, if he hits his target, he scored. This term is heavily by gang members in Chicago drill music.
Score is as a slang term to describe items in a robbery.
Score is used as a slang term to describe the transfer of illicit substances. For example a fiend purchasing some ecstasy pills might go back to his friends and say "I just scored some flats."