Reddit glossary
What is Crosspost on Reddit?
A crosspost is a post that is shared from one subreddit into another, with a link back to the original.
It lets you show the same post to a different community without copying it by hand. The original author and community stay visible.
Some communities do not allow crossposts, and others only allow them from certain places.
If you are promoting something
Do not crosspost the same promo to many subreddits. It looks like spam. If you share something, write it fresh for each place.