Yes, I would say the most common definition is: "Homosexual".
Most english-speaking adults know that another definition is "happy", but I personally have never heard anybody use it that way in a sentence. Only in literature.
In America some people, especially young people, very informally, use "gay" to mean "poor quality, stupid or ridiculous". Examples: That movie we saw was so gay!" Meaning it was stupid or poor quality. But this is not really an acceptable way to use it. It think that is what Erica means.