If you see it on this site, it might refer to the division of language. For example, you could be looking for someone to chat to, half the time in Chinese and half the time in English.

It refers to the division of responsibility, usually. If one person pays 50% of the cost of something, and a friend does the same, they have paid 100% for the thing. Other than money, it can refer to equal sharing of work and so forth.

i believe it refers to the division of genre, 50/50 students: 50% women/ 50% men.