An online community member who reads posts but does not comment is called a lurker. The term describes someone who observes discussions without publicly contributing, whether on a forum, mailing list, chat community, social network, or support site.
Lurking is not necessarily hostile or antisocial. New members often read first to learn a community’s vocabulary, etiquette, recurring topics, and influential participants. Someone may also lurk because browsing provides enough information, because they want to avoid repeating an earlier point, or because they are deciding whether the community is a good fit.
The term is sometimes contrasted with “poster” or “contributor,” while “flamer” describes someone who posts hostile attacks and “spammer” describes unwanted promotional or repetitive posting. A lurker may eventually begin participating; that transition is often called “de-lurking.” Because lurkers leave few public traces, they can be difficult to measure, but they may form most of a community’s audience.