A song or piece of music that doesn't appeal to a person on first listen, but after a while "grows" and becomes enjoyable in time. This is a common occurrence.
"At first I didn't like SONG A at all, but now after a week or so of listening, I love it. It is a grower (song)."
A grower is someone who's dick looks tiny when soft but gets to a much larger size when hard. A shower is someone whose dick is already most of the full size soft and basically just solidifies when hard.