It appears in many English words, often related to emptiness, absence, or lack of something:
* Vacant: empty, unoccupied
* Vacation: a period of time free from work or school
* Vacuum: an empty space, a device for removing air and dust
* Evacuate: to empty or withdraw from a place
* Vacuous: lacking in intelligence or meaning
* Vacillate: to waver or fluctuate
The meaning of "vac" can sometimes be slightly different depending on the specific word, but the core idea of emptiness or absence is usually present.