lurking
Lurking is the very common practice of reading an online or e-mail discussion without taking part in the discussion. Most visitors to discussions on Web sites, Usenet groups, e-mail discussion groups, Internet Relay Chat channels, or bulletin board systems understandably spend much more time reading or "listening" than writing or "speaking." What this term seems to imply in its usage is that some people benefit a great deal from a discussion without ever offering to enrich it with their own information or ideas. It is well understood and accepted, however, that there will always be lurkers in any discussion. And people new to a discussion are sometimes advised to lurk until they become familiar with the discussion.