Think there is undershot and overshot, think under is when bottom jaw sticks out more than top, over is when teeth stick out too far. (could be wrong),
My son is awaiting his brace - he has a mix of the two! One tooth is behind bottom row, one is too far in front - symptom of overcrowding and 'funny' jaw shape I suppose there must be a doggy equivalent too.
(Sorry posted same time as JaneS)