To deflate means to let air or gas out of something that was inflated, like when you open the valve on a bicycle tire and watch it slowly go flat. You might deflate a beach ball before packing it for a trip, or deflate a balloon after a party ends. When something deflates, it shrinks down and becomes soft and floppy instead of firm and round.

The word also describes what happens to someone's confidence or excitement when they receive disappointing news. Imagine working hard on a science project you're proud of, then having a classmate point out a major error. Your enthusiasm deflates: that excited, energetic feeling collapses like air rushing out of a balloon. A teacher might say that criticism shouldn't deflate students, but should help them improve. When someone feels deflated, they've lost their energy and optimism, at least temporarily.

In economics, deflation means prices are falling rather than rising. This might sound good at first, but it can cause serious problems for businesses and workers. Economists worry about deflation because it can slow down the whole economy, though this meaning is less common in everyday conversation.