1. a person who reads online discussions or forums without participating or posting
Usage: internet slang
2. a person who hides or waits in a concealed place, especially with harmful intent

Examples

• Many lurkers read the forum daily but never comment.
• She was a lurker on social media, following conversations without joining in.
• The website analytics showed thousands of lurkers for every active user.
• Police warned residents about a lurker spotted near the school.
• He remained a lurker in the chat room for months before finally posting.
• The security camera caught a lurker hiding behind the building.