[X marks the spot] An indication made on maps or documents […]

[x-double minus] {adj.}, {slang}, {informal} Extremely poorly done, bad, inferior (said […]

[x-rated] {adj.}, {slang}, {informal} Pertaining to movies, magazines, and literature judged […]

[x-raying machine] {n.}, {slang}, {citizen's band radio jargon} Speed detection device […]

[X\> *] Definition of something X as better than everything *. […]

[XD] An emoticon resembling someone laughing when rotated clockwise 90 degrees. […]

[Xerox Subsidy] Euphemism for swiping free photocopies from one's workplace.

[xOMG] OMG^3

[yak-yak] or [yakety-yak] or [yakib-yak] {n.}, {slang} Much talk about little […]

[year] See: [ALONG IN YEARS] or [ON IN YEARS].