I've watched the show like literally two times but i have a lot of friends who looove that show xD Of course the word GLEE means like joy and happiness and it makes sense since the show is a highschool comedy musical lol so theres a lot of moments on the show where theres dancing and singing while dealing with the lives of teens in highschool . In that school the band group are basically what are known as the "glee club" :P and the main characters of the show lol

Glee Meaning and Definition (n.) Joy; merriment; mirth; gayety; paricularly, the mirth enjoyed at a feast. (n.) An unaccompanied part song for three or more solo voices. It is not necessarily gleesome. (n.) Music; minstrelsy; entertainment.