In economics, when prices drop it's called deflation. Deflation makes money more valuable — prices are lower, so you can buy more with it. But deflation is also what happens to a tire if it runs over a nail. Bummer.
When economists talk about inflation, they mean that prices are very high, and it takes more cash to buy things. Deflation is the opposite—it's also known as a negative inflation rate. Deflation is dangerous for the economy, and it's connected with era like the Great Depression of the 1930s. Deflation literally means "a loss of air," and you can use it that way too: "The deflation of my tires meant I wasn't going anywhere."