Abbreviation of back.
"The new video game released early access for PS5 and Xbox Series X, but it wasn't available on PC until a month later."
A Korean surname, from Korean, the English form of a surname very common in Korea. (박 (Bak), hanja: 朴). The third most common Korean surname.
"After successfully completing their bak, Maya felt ready to begin her practical flight training maneuvers under the instructor's supervision."
Initialism of Basic Aeronautical Knowledge., an initial theory course for trainee pilots.