1. To gather closely around someone or something. In this usage, "crowd in" can be followed by "on" and then a particular person or thing. When the teacher announced story time, the kids all crowded in. I hate when people crowd in on a buffet as soon as it's served.

2. To fill a space with more than it can reasonably hold or accommodate. In this usage, a noun or pronoun can be used between "crowd" and "in," and "into" can be used instead of "in." We can't crowd anyone else in, unless we move the lecture to the auditorium.

3. To push one's way into a certain place or area. In this usage, "into" can be used instead of "in." We tried to crowd into the lecture hall, but the professor told us it was filled to capacity.