| Idiom | Meaning | Example |
| X Generation | (See Generation X) | |
| x marks the spot | look for x, begin at x, x is important | Someone had written on the map "X marks the spot where we were abducted by aliens." |
| x-rated | for adults, for a mature audience | Born Loose is an x-rated video. It contains nudity and sex. |
| XL | extra large or very large, extra luxury or extra power; shirt - size XL, car - 300XL | "This shirt is marked XL. What does that mean?" "It means extra large. On cars, XL means extra luxury or power." |