Mega means extremely large or great. When something is mega, it's impressively, unusually big. A mega sale at a store offers huge discounts. A mega hit song gets played everywhere, all the time. Your friend might describe an incredible birthday party as mega fun.

Scientists use mega as a prefix meaning one million: a megabyte is one million bytes of computer data, and a megawatt is one million watts of electrical power. When paleontologists discovered fossils of an enormous prehistoric shark, they named it megalodon, combining mega with the Greek word for tooth.

In everyday conversation, mega often appears as slang meaning “very” or “really.” Someone might say “that test was mega hard” or “I'm mega tired.” While this casual use isn't formal English, it captures the word's essential meaning: making things sound bigger, stronger, or more intense than usual. Whether you're describing a megastructure like a massive dam or just a mega-sized pizza, the word adds impact and emphasis.