They were already calling them zaps before that, not that I care anyway.

btcphoto

they are called zaps because they also show the cumulative tipping amount and each user who left a tip on a specific note

nextblock

nostr

deleted by author

tenderscore

For me zaps are just the new way to call instant lightning tips with a press of a button, like here in Stacker News. I think the first time I read it called zaps was from the people of Starbackr. 

On Nostr the amount zapped in a post will appear only if the poster has NIP-57.