What's this mysterious button on the Switch controller?

There's one button on the Switch controller that has people scratching their heads. You can see it in the image above. Just what does that button do? It doesn't look like a power button, as it doesn't have the traditional logo that Nintendo used on the Wiimote and Wii U GamePad. We did hear a rumor awhile back about a 'Share' button being on the controller. Could that be what we're looking at? Perhaps it's even something amiibo related. We don't know yet, but we'd love to hear your speculation!