「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(はん)分(ぶん)は全(ぜん)体(たい)を二(ふた)つに分(わ)けた一(ひと)つ。ケーキを半(はん)分(ぶん)食(た)べました。