The OP, or "Original poster", is the author of the post. You can spot an OP within a post thread if they have a microphone next to their username. Admins are distinguished with a Snoo icon or an "[ A ]" next to theirs. A green-colored username is a universal marking of a Moderator with a "[ M ]" next to it if you’re on Old Reddit and a shield () on New Reddit. Some subreddits support unique flairs for mods, and you can also generally find the list of moderators in the column on the right side widget in the subreddit.