When something is very, very, VERY big, it can be called enormous. “Good heavens, that pimple on your cheek is absolutely enormous; it covers half your face!”
The word enormous contains within it, if you look closely, the root norm, as in normal. So what you’re saying when you call something enormous is that it’s beyond what is normal; you’re trying to convey a sense of exaggerated difference. You may also have heard the word ginormous, which people try to use as enormous with a dramatic flair. But, trust us: ginormous is not a good word; it’s just a blend of two words — gigantic and enormous.