Overbite and overjet describe the relationship of the upper and lower front teeth to each other.
Overbite is a vertical dimension and it relates to how much of the lower front teeth are covered by the upper teeth when a person bites together. When the bite is very deep and the bottom front teeth hit on the gum tissue in the roof of the mouth, that condition is called an impinging overbite.
Overjet is a horizontal dimension and relates to how much the upper teeth stick out or jet out over the lower teeth.
When you do not have any vertical overlap of the front teeth when you bite together, that’s called an openbite. The back teeth bite together, but the front is open. This condition can result from thumb sucking.
It is further confusing because you want to have some vertical overlap (overbite) and you want the top teeth to be forward to the lower teeth when you bite together (overjet). You want a scissor action with the front teeth, so when you bite the sandwich, you get the lettuce. Orthodontics can be used to treat and improve both conditions.