I want to know, too. "Zap" popping up everywhere, but nowhere anyone who explains systematically what it is for the newbs.
Discussion
Seems to be a shortcut for paying a Lightning invoice, by a button attached to each note in (among others) the Testflight version of Damus. Likely even tighter integration coming soon. Right now it still calls an external wallet with the Lightning address of the one who posted the note (provided they have one on their profile).
