This excerpt taken from the MRO DEF 14A filed Mar 10, 2005.
o What are broker non-votes?
The New York Stock Exchange permits brokers to vote their customers' shares on routine matters when the brokers have not received voting instructions from their customers. The election of directors and the ratification of independent auditors are examples of routine matters on which brokers may vote in this way. Brokers may not vote their customers' shares on non-routine matters such as the stockholder proposal to declassify the Board of Directors, and the stockholder proposal to elect directors by a majority vote, unless they have received voting instructions from their customers. Non-voted shares on non-routine matters are broker non-votes.