1. people who read online discussions or forums without participating or posting
Usage: internet slang
2. people who hide or wait in concealment, especially with suspicious intent

Examples

• The forum has thousands of lurkers who never comment on posts.
• Many lurkers eventually become active members of online communities.
• The moderator encouraged lurkers to introduce themselves.
• Security cameras caught several lurkers near the building at night.
• Police warned residents about lurkers in the neighborhood.
• The lurkers disappeared when the lights came on.