What does "ivory" mean in this case?

Native speaker’s answer
Rebecca
In the past, ivory was used to make the tops of piano keys (the white keys). They were called "ivory keys." It's no longer done now, however. The speaker has probably said "ivories" here as a funny, cute way to refer to the keys of the man's instrument. By saying "tickle those ivories," he's telling him to start playing the song. You definitely wouldn't hear people refer to keyboard or piano keys in this way normally. Ex: Wipe down the keys after you practice. You want your piano in the best condition. Ex: Look at the way her fingers dance across the piano keys.