Music, typically that mainly uses simple words, catchy melody, rhyme and repitition. It usually, but not always is old, well known and still in the mainstream. Unlike contemporary R&B, pop and electronic, it uses soft acoustic sounds mainly, and drumming on rare occasions. We can say that the opposite of children's music is rap-metal. Rap-metal is a fusion genre that combines either hip hop or rap with any metal genre (funeral doom, black metal, doom metal, death metal, heavy metal, etc.)

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.