"Beta" is really just the second print-run of the first set of Magic: The Gathering. But the Beta cards are noticably different because they have much less rounded corners (as have all Magic sets since then).

Have you ever wondered what the difference is between Alpha and Beta? Well... other than the the fact that Alpha has more rounded corners, there is only a difference of seven cards. Beta has Circle of Protection: Black, Volcanic Island, and one more of each basic land, for a total of 302 cards.