Reddit glossary
What is Shadowban on Reddit?
A shadowban is when your posts or comments are hidden from everyone else but still look normal to you.
People use the word loosely. Sometimes it means a sitewide action by Reddit. More often a spam filter in one subreddit is quietly removing your content.
A simple check is to open your post in a private browser window while logged out. If you cannot see it there, other people probably cannot either.
If you are promoting something
If you think you have been filtered, stop posting and read the rules. Do not make a new account to get around it. That is ban evasion and it makes things worse.