Olympus is first the home of Cronus and the Titans, then after the Titanomachy the home of Zeus and the Olympians. It seems certain that Olympus was originally considered to be the actual mountain Olympus, which is located in Thessaly and is the tallest mountain in Greece. Later, as perhaps Mt. Olympus was climbed, it seems to have become a place in the heavens above Mt. Olympus.
Oxford Concise Companion to Classical Literature. ed. Howatson and Chilvers. Oxford. New York, 1993.