The term object is either a Player, Thing, Exit, Room, or Garbage. These objects have attributes including a name (see @name command), and a unique number called a dbref which is short for database reference. Used together these objects form a grid of rooms interconnected with exits with players and things contained within them, things inside players, and players inside things. Location is therefore one of the relationships, but there are other relationships as well including ownership and parentage.
Confusingly, sometimes a thing is referred to as an 'object', or as a 'regular object' (because things are sometimes seen to miss any specific traits the other types have).