1) Half off / 50% off 卖半价，打五折
Oooooh! Did you see? All these lipsticks are half off!
Should I get these shoes? They're 50% off!
2) BOGO Buy One Get One / two for one 买一送一
A lot of stores are having BOGO sales right now! Let's go shopping!
Let's go to Gap! They're having a two-for-one sale!
These shirts are two for one. I think I'm gunna get a couple!
3) Coupon 折价券
Oooh, I got a coupon for $25 off of my next purchase of $50 at this restaurant.