「半分」 (hanbun) means "half." You use it to indicate one of two equal parts of something. It can refer to quantities, portions, or even a period of time. For example, 「ケーキを半分食べました。」(Kēki o hanbun tabemashita.) means "I ate half of the cake."

半分は全体を二つに分けた一つ。ケーキを半分食べました。