Facebook is updating new feature 'Hello'

Facebook is reportedly testing a 'hello' option which lets users get others attention by sending a virtual wave, much like the Poke option. It was made available to only a few users.

The below image is might be a sample which shows along with friend request. Incase if you accedentally tapped on HELLO, you can undo it by tapping on it again and hitting the Ok that pops up.