Proportional Allocation is a mathematical criterion governing the way vote weight is spent as candidates are elected in sequential proportional representation voting methods. Ranked voting methods which pass the Proportional Allocation Criterion ensure that a voter can not spend their entire vote on a less preferred candidate while a more preferred candidate is still in the race. Score voting methods which pass the Proportional Allocation Criterion ensure that a voter can not spend more of their vote on a candidate than their level of support for that candidate.
Proportional Allocation: The cost to elect a candidate shall always equal the amount of support given to that candidate minus the voter's share of any surplus votes received by that candidate. For example, a voter who gave a candidate 3 out of 5 possible stars can only spend a maximum of ⅗ of their vote on that candidate.
Note that for ranked methods which don't allow voters to show their level of support, the cost to elect a voter's top-ranked remaining candidate must always be that voter's full support minus their share of surplus votes received by that candidate.
Surplus votes are defined as any votes received by a candidate in excess of the quota of votes needed to win a seat.