Off the top of my head, these are some of the phrases, words, abbreviations, and acronyms that have non-obvious meanings…
… on Wikipedia: barnstar, nom, toolserver, rollbacker, checkuser, oversight, bureaucrat, steward, mainspace, arbcom, portal, gnome, Huggle, Twinkle, FA, FAC, FAR, GA, GAN, GAR, RfA, RfB, RfC, RfCU, BAG, DYK, ITN, PR, SPA, NPOV, 3RR, AGF, MOS, RS, AWB
… in theater: fly galley, arbor, batten, fresnel, Source Four, electric, Edison connector, twofer, traveller, teaser, cyc, scrim, pit, flat, scab, drop, tech, Equity, practical, paints, carps, sight line, Genie, green room, hang tape, pick point, barn door, top hat, iris, mover, strike, PAR, ETC, DMX, XLR, IATSE, LX, ME, LD, PA, ASM
… at Walt Disney World: Protein spill, honey bucket, friends with [name], Munk height, Disney height, Disney look, Disney point, bid, spare, color code, step-off, step-down, walk time, cast member, character base, grouper, breaker, PC, CP, ER, 101, MOUCP