When you eat something, it might taste really good at first, but after you swallow it, you might still feel like you can taste it in your mouth. That's called an aftertaste! Sometimes aftertastes are good, like when you eat a piece of candy and the sweet taste lingers in your mouth. But other times, aftertastes are bad, like when you eat something really spicy and it burns your mouth even after you're done eating it.
Aftertastes happen because the food you ate left small particles or chemicals behind in your mouth. Even though you can't see them, they're still there and they can continue to make your mouth taste a certain way even after you're done eating. Some foods or drinks can create stronger or longer-lasting aftertastes than others, and some people may be more sensitive to aftertastes than others. So, aftertaste is like the taste that stays in your mouth even after you finish eating or drinking something.