A makeup product, usually used by women to cover up dark eyebags or lightacne. The reason it's called that, is beacuse it originally came from the word conceal, which means to hide something.
PERSON 1: ugh i hate my eyebags!!!
PERSON 2: i have some concealer, wannaborrow some?
Those shirts that girls always wear that are tights at the top and then flow out over their muffin top. They think they are tricking you and hiding the muffin top that lurks under those folds of fabric.
Guy 1: That girl over there is hot Guy 2: That's because she is wearing a muffin top concealer and her muffin top is hidden.
Guy 1: Touche