- Initialism of Global Telecommunications System, a worldwide network for the transmission of meteorological data from weather stations, satellites and numerical weather prediction centres.
- General Theological Seminary
- Gilles de la Tourette syndrome
- Great Trigonometric Survey
- green tobacco sickness
- Greenwich Time Signal
- geologic timescale
- (Internet) Giantess (as a sexual fetish).
- 1997, "Wilfred D. DeVoe", Addresses of GTS & Tall Woman sites (on newsgroup alt.sex.fetish.size)
- 1999, Katharine Gates, Deviant Desires: Incredibly Strange Sex
- INTERNET SEARCH KEYWORDS: GTS, macro, giantess, crush, trample. WHAT IT IS: A sexual fantasy of being tiny and at the mercy of a gigantic human.
- 2006, Dominique Mainon, James Ursini, Modern Amazons: Warrior Women on Screen
- Technically the erotic obsession with such large women is labeled "macrophilia," but it is more commonly referred to as simply "GTS," short for giantess.