It is a new electoral system proposed for Ontario. If you are voting in the upcoming Ontario Provincial Election on Oct 10, 2007, There will be a referendum question asking if you want to keep the current system or change to use MMP.
With the proposed MMP in Ontario, you will vote for a local candidate and a party - it's that simple.
Then, when the votes are all tallied, if a party has proportionally less seats than the percentage of the overall vote they received, they get additional general party seats known as List seats. So, in the end, the number of seats a party has in parliament, is directly proportional to the percentage of votes they received.
Example: If party A received 40% of the vote, then they get 40% of the seats.