When, during oral sex, the penis only reaches the back of the mouth & doesn't ever enter the throat. This could be due to the penis being too short or the girl refusing to take it deeper.
"She's terrible at blow jobs... She tried to give me head, but she refused to deep throat me, I got some 'back mouth' at best!"
When, during oral sex, the penis barely crosses the threshold of the throat. The most shallow form of throat penetration.
"Dude, how was last night? That bitch give you some deep throat?" ... "Nah man, I barely even got short throated, she couldn't handle it."
When, during oral sex, the penis barely enters the mouth and stays in the front of the givers mouth.
"Damn man, that girl must have the strongest gag reflex ever, she only let me get front mouth."