1. To form or get into a specific kind or size of line. OK, everyone, line up in a single-file row and follow me into the auditorium. We lined up in a semicircle so we could all hear what the coach had to say.

2. To cause or direct someone or something to form or get into a specific kind or size of line. In this usage, a noun or pronoun can be used before or after "up." Make sure you line the products up in groups of five—they tend to sell better that way, for some reason. The boss lined the three of us up in a row so he could scold us all at once about our performance on the project.

3. To form or get into a line inside of some place or thing. We all lined up in the box office to collect our tickets for the play. The baby birds lined up in their nest to receive food from their mother.

4. To cause or direct someone or something to form or get into a line inside of some place or thing. In this usage, a noun or pronoun can be used before or after "up." The teacher lined his students up in the back of the classroom so he could see who was the tallest and the shortest. Line up these boxes in the warehouse, and we'll sort through them later.