Not contradicting you Mario, but the word I like best to describe it is "resonance". Songs do stay with you for different reasons and with some of them the context is everything. Of course, songwriters do their damndest to make a song keep coming back to you after you have heard it. Hooks, rhymes, imagery, rhythm are all part of our tool kit. If the song keeps coming back to you though, you don't need to be able to identify which which tools and materials went into its making. I reckon that if it keeps playing in your head - and you want it there - for you it is a good song.