Definition of "predrinks"

Neither Bob nor Dorothy showed up for predrinks at the producer′s home.

1998, George Eells, Robert Mitchum: A Biography

I was thinking to have had an initial predrinks meeting-up phase in the North-End pub (everybody knows where that is,right?) starting at 18:00, and then have had dinner around seven fifteen at the Illegale, and after that have gone back to the North-End.

1998 September 16, Patrick 'Turtle' Dersjant, “[F] Dutch Pre-Con Minimeet”, in alt.fan.pratchett.announce‎ (Usenet)

Predrinks will still remain the best option for myself ... I didn't stock up a fully equipped bar with a selection of each of my favourite spirits and liquers and beers for nothing :)

2000 February 11, Ammorata, “Melbourne's goth scene from a Canberran perspective...”, in aus.culture.gothic‎ (Usenet)

Predrinks at Slug and Lettice[sic], very near Canary Wharf Jubilee Line station from 7pm, leaving 7.30pm(ish) to make our way over to Crossharbour.

2002 December 20, Paul G, “Have I missed Christmas?”, in uk.gay-lesbian-bi‎ (Usenet)

It's the only country I have been in where everybody, and I do mean everybody, arrives at the pub in a state of total intoxication and proceeds to drinking like fish. The predrinks are done as the off sales prices are reasonable whereas bar prices caused me to nearly faint but arriving drunk numbs that effect.

2007 August 4, Cerumen, “Harry Potter and the Monumental Cock-up”, in uk.rec.sheds‎ (Usenet)