tri 5 chevy

Alright to start off with I will say I have never been a huge fan of the 1955ish chevys. Too angular for my personal taste. I prefer the swoopy lines of earlier cars. So that might explain why I have to ask such a simple question.

Why do they call these cars (55 and up) chevrolets tri 5's???

Thanks

 

55 , 56, and 57 chevys had the same basic lines and shared parts..

 

55-56-57 equals 3 which is tri (3)