A quick definition of fill a blank:

Fill a blank: In parliamentary law, filling a blank means to replace an empty space in a motion with one or more suggestions from the floor. It is like a puzzle where people suggest different pieces to complete the picture. It can also refer to a ballot cast without a vote or a term left open in a motion to be filled in by a vote after taking proposals from the floor. For example, during an election, each nomination is a proposal for filling the blank in the question, "Resolved, That _______ is elected."