YHA is short for the Youth Hostels Association, the British organisation that runs youth hostels — cheap, simple places to sleep, often with bunk beds in a shared room and a shared kitchen, made for walkers, cyclists and travellers who do not have much money. It belongs to the worldwide network (Hostelling International), so other countries have their own YHA too — Australia and New Zealand use the same three letters. You say the letters one by one: Y-H-A. People use it in three ways in ordinary speech. First as the organisation itself: "the YHA raised its prices." Second as a name for a building: "we stayed at the YHA in York." Third as a describing word in front of another noun: a YHA hostel, a YHA card, YHA membership. Historically you had to be a member to stay, and older people still talk about "joining the YHA"; these days anyone can usually book, and members just pay a bit less. The word has a slightly old, wholesome feeling for British people — school trips, hiking boots, rain. Note that although the name says "youth", adults and families stay in YHA hostels all the time; nobody is turned away for being fifty.

（英國）青年旅舍協會；YHA 青年旅館（就是背包客住的那種便宜旅舍）