The standard Kit Kat bar sold in most countries is made up of four wafer fingers. Each finger is a separate layered wafer covered in chocolate and can be snapped away from the rest of the bar.
Kit Kat was created by Rowntree's of York, England, and the original four-finger bar launched in 1935 under the name Rowntree's Chocolate Crisp. It was renamed Kit Kat Chocolate Crisp in 1937 and later shortened to Kit Kat. Nestlé acquired Rowntree's in 1988, bringing the global brand under Nestlé ownership.
The four-finger format was inspired by the idea of a chocolate bar that could be carried in a worker's lunch pack. A two-finger version followed in 1936 and remains an important format, so not every Kit Kat has four pieces.
The question says “most countries” because Kit Kat sizes vary by market. Some versions have two, three, five, eight, or even twelve fingers, while Chunky bars use one large finger. In the United States, Kit Kat is produced under licence by Hershey, but the global brand is associated with Nestlé.