1. noun An expression of greeting, support, or congratulation by slapping another person's hand with one's own at or around waist level. I gave him a subtle low five for making such a witty joke at the teacher's expense. I went to give her a low five, but she pulled her hand away at the last second.

2. noun To slap another person's hand with one's own at or around waist level as an expression of greeting, support, or congratulation. The player ran along the ranks of her teammates as she entered the field, low-fiving each of them as she went.