r

"R" or "r" as a letter indicates readiness. Its origin started when joining a queue in competitive online gaming, and this slang recently transitioned to be used in other settings.

"R" can be used informally or formally let someone know that you're ready to commence in whatever activity was previously stated.

1) Alright.. Everyone here? I'm going to queue us for a 5-man!

Response: r

2) Hey - I'm going to be a few minutes late to the meeting.

Response: NP! We're here when R.