noun
Refers to a sales event or discount period, as in a store sale. Not used for the act of selling in general.
デパートで夏のセールが始まった。
The summer sale has started at the department store.
セール中にこのコートを買った。
I bought this coat during the sale.
バーゲン also means 'bargain sale' and is often used interchangeably with セール, but バーゲン can imply a particularly good deal or clearance event.
Loanword from English 'sale', adopted into Japanese with the meaning of a discount sales event.