This excerpt taken from the AAPL DEF 14A filed Jan 23, 2008.
For business to be conducted at the Annual Meeting, a quorum must be present. The presence at the Annual Meeting, either in person or by proxy, of holders of shares of outstanding common stock entitled to vote and representing a majority of the voting power of such shares will constitute a quorum for the transaction of business. Abstentions and broker non-votes (i.e., shares held by a broker or nominee that are represented at the Annual Meeting, but with respect to which such broker or nominee is not instructed to vote on a particular proposal and does not have discretionary voting power) will be counted for the purpose of determining whether a quorum is present for the transaction of business. If a quorum is not present, the Annual Meeting will be adjourned until a quorum is obtained.