In the United States, a "vacation" usually means a trip away from home, taken for pleasure. A weekend would only be a "vacation" if you left your home.
Often, a "vacation" is a period of two or three weeks. If you are only leaving for the weekend, one might say "a weekend vacation," "a mini-vacation," or simply "we're going away for the weekend."
(The fundamental meaning of the word is to go away from a place, such as your home, leaving it empty. When school closes for the summer and the students leave, it is a "school vacation" because the school is empty of students).