The acronym givin to 'hot chicks' seen out of a school environment.
Cooler Than All The Chicks At School
Sometimes the final letter of the acronym can be replaced by the first letters of the name of a school.
BH = Balwyn High
guy 1: saw a totally smokin chick at the movies
guy 2: was she CTATCAS ??
guy 1: fo sho brother!