What determines which genre a song/group falls into? As an example, I'm a fan of the Carpenters. While most of their music falls into the "Easy Listening" genre, they did some songs that fall into other genres such as "Sweet Sweet Smile" (country), "B'wana She No Home" (jazz), and "Calling Occupants Of Interplanetary Craft" (symphonic rock).
I did some checking in Wikipedia and found a list of a massive number of musical genres. Still, how do you determine which genre a specific song falls into? Even more confusing are parodies, do you put them in the genre of the original song, or do you treat them as comedy?