Rashi on Exodus
בקע (from בָּקַע to split) is the name given to a weight of half a shekel.
Siftei Chakhamim
This is the name of the weight . . . Rashi is answering the question: Does בקע not mean “splitting” throughout Scripture? But here, “splitting” does not fit as a meaning.
Chizkuni
בקע לגלגלת, beka, per head (half a holy shekel). The people relied on G-d being aware that this amount would suffice for the silver needed in connection with the Tabernacle.