1. To identify with a particular number in a sequence. The students all numbered off, and the teacher grouped everyone with an even number on one side of the room while everyone with an odd number went to the other side. We numbered off in sets of five for the group activity.

2. To assign someone or something with a particular number in a sequence. In this usage, a noun or pronoun can be used between "number" and "off." The coach numbered the players off into groups of five to practice different drills in rotation for the rest of the day. The class is too big to do the work all together, so we'll have to number off the students and have them complete the assignment in smaller groups.