Lurker (noun)

1. A person who regularly reads messages in an online forum or social media platform but rarely or never participates in the discussion.
2. A person who is present at an event or location but does not participate or engage with others.

Origin:

The word lurker is believed to be derived from the verb "lurk" which means to hide or stay hidden.

Examples:

1. He was just a lurker on the online forum and never posted any comments.
2. She was a lurker on social media and only watched the posts of her friends.
3. The lurker followed the group through the woods without making a sound.
4. The lurkers in the back of the room made the speaker uncomfortable.
5. He was a lurker in the chatroom, reading the messages without ever writing anything.