They describe a leaderboard built from server members' shared gaming activity, while actual rollout remains unconfirmed.
When It Appears
“{days}d left” can appear on a server view that ranks shared gaming activity and shows a timed competition when Discord displays the number of days remaining in the current competition.
What It Means
When “{days}d left” is shown, the current step is presenting the number of days remaining in the current competition.
A user who saw “{days}d left” in Discord is likely searching to confirm that it means the number of days remaining in the current competition, where it appears, and which state it describes.