ROLLBACK AFTER integer [SECONDS] | ROLLBACK IMMEDIATE
Specifies whether to roll back after a specified number of seconds or immediately.
NO_WAIT
Specifies that if the requested database state or option change cannot complete immediately without waiting for transactions to commit or roll back on their own, then the request will fail. If you have understood the difference by now, there is no need to proceed further. If you are still confused, continue with the rest of the post.
Read more: Journey to SQL Authority with Pinal Dave