Hat Yai Vacations, Hat Yai Vacation Reviews, Tourism Guide

Hat Yai (also known as Haad Yai / Had Yai) is a city in southern Thailand near the boundary to Malaysia.
Geographical location 7°1′N, 100°28′E. With a population of 155,585 (2005) in the core city and about 300,000 in the Greater Hat Yai, Hat Yai is the biggest city of the Songkhla Province and the largest metropolitan area in Southern Thailand, and is thus often mistaken as being the capital of the province. However Songkhla is the capital, unlike the other provinces where the capital is the biggest city of the province. The city covers the whole tambon Hat Yai of Hat Yai district. Both cities are a part of Greater Hatyai-Songkhla Metropolitan Area.

The name "Hat Yai" is a short version of "Ma Hat Yai", meaning giant Ma Hat tree

(taken from Wikitravel)