1. To stand in a row next to other. The teacher asked us to line up alongside each other so she could see who's taller and shorter. The impact of the recession really hit me when I was there lining up alongside friends and relatives to collect my social welfare payments.

2. To cause someone or something to form or get into a row next to others. In this usage, a noun or pronoun can be used before or after "up." The coach lined me up alongside the other students trying out for the football team. I've been lining up my DVDs alongside my collection of VHS tapes.