1) A conversational term used when everyone in a convo knows what you're getting at, but you're starting to come off the tracks.
2) A term used as a placeholder, like a variable in mathematics. Best used when rhythm is more important to a sentence than details.
1)
"So, when she and I started getting hot and heavy, she reached down and uh, she. Sigh. Fair catch"
2)
"I stapled the fair catches to the wall so that you can't miss them when you sober up."
"Move the green fair catches across the map so you don't have to worry about getting flanked"