The story
Initialism of under the gun. From the fact that being UTG (i.e., the first to play) is often considered a strategically disadvantageous position.
Etymology from Wiktionary, CC BY-SA 4.0.
UTG
Today it means: Sitting to the left of the big blind (BB), thus being the first to play in many varieties of poker, including Texas hold 'em and Omaha. Full definition →