Think of inflation as expansion, usually from being filled with air, like a balloon. This also refers to rising prices.
Think of a balloon puffing up, getting fuller and fuller — that's inflation. The word has a bunch of related meanings. We can say people a little too full of themselves are suffering from inflation: they are full of hot air. When the cost of living is ballooning, that's economic inflation. When the universe was born in the big bang, there was a huge inflation, as matter spread out, creating galaxies, stars, and planets.