A ping is when you get mentioned on Discord. Most users hate this.
Example: "@superCoolUsername#1234 haha i ping you"
Ping is a command, typically on a selfbot (bot of a user Discord account (against Discord's TOS (Terms Of Service))), used to see how long a request took to get to the server the bot is hosted on. Many selfbots have been found, either accidentally or intentionally, using this method on the Replit Discord Server.
veryUncoolSelfbot 🏓Pong! 532 ms
(the image used in this entry was a joke)