Clans and Bloodlines
A Clan in Vampire the Masquerade is used to describe the major groups of vampires who share common characteristics that are passed down through the embrace. These are typically similar abilities and weaknesses.
A Bloodline is a subset of a Clan that is a smaller group of vampires who still have the majority of the common abilities and weaknesses of their parent Clan, but with changes significant enough to be noted. This is normally a slight tweak to abilities and/or additional weaknesses, with some historic cause.