noun
20 percent
Used for expressing a 20% proportion, discount, or ratio. 割 is a unit meaning 10%, so 二割 is 2 × 10%.
この商品は二割引きです。
This item is 20% off.
参加者の二割が女性だった。
Twenty percent of the participants were women.
割 is the unit for 10%; 二割 is 20%, while 割 by itself can mean proportion or 10%.
パーセント is the loanword for 'percent'; 二割 is the native Japanese way to say 20% and is more common in everyday speech for discounts and ratios.
Compound of 二 (two) and 割 (unit of 10%). The 割 unit derives from the verb 割る (to divide), referring to a tenth part.