Green’s Dictionary of Slang

gath n.

[SE gathering]

(UK black) any form of get-together, indoors or in a public space, e.g. a park.

hubpages.com ‘Roadman Slang 10 Jan. 🌐 Gath - short for ‘gathering’, this word describes a general drinking event that isn't someone's birthday or a special event. These casual nights take place in parks and houses, and rarely consist of more than 15 people.