What makes a song "gay?"

Is it the singer's real-life sexual persuasion, the explicit or implicit (and positive or negative) lyrical content, how it has been embraced by the gay community, being inextricably linked with its homo-erotic video...or something else?

Or all of the above?

"Wait...'YMCA' is about more than just hittin' the gym?"

My picks for the gayest songs of all time follow below in alphabetical order by artist. There is also a separate post (with a crazy load time) with the songs arranged somewhat creatively for your listening/viewing enjoyment.

Feel free to tell me what am I missing, in both senses of the question...