The Thirtieth of September Movement (, abbreviated as G30S, also known by the acronym Gestapu for Gerakan September Tiga Puluh, Thirtieth of September Movement) was a self-proclaimed organization of Indonesian National Armed Forces members who, in the early hours of 1 October 1965, assassinated six Indonesian Army generals in an abortive coup d'état, resulting in the unofficial but more accurate name of Gestok, for Gerakan Satu Oktober, or First of October Movement."The assassination of generals on the morning of 1 October was not really a coup attempt against the government, but the event has been almost universally described as an 'abortive coup attempt,' so I have continued to use the term.

-30- has been traditionally used by journalists in North America to indicate the end of a story or article that is submitted for editing and typesetting. It is commonly employed when writing on deadline and sending bits of the story at a time, via telegraphy, teletype, electronic transmission, or paper copy, as a necessary way to indicate the end of the article.

In Major League Baseball (MLB), the 30–30 club is the group of batters who have collected thirty home runs and thirty stolen bases in a single season. Ken Williams was the first to achieve this, doing so in 1922.