1.To open your awareness.
2.Something that just interest you or makes you happy.
Not just a sexual term. Anyone from the 60's used this term prevalently through out the grooviest time in our recent history.
Timothy Leary "Turn on, Tune in, drop out."
ex1: The warm weather today is such a turn on.
ex2:I just got Turned on by this guy to Jefferson Airplanes album.