Those who observe the activities of an online community without engaging themselves are colloquially known as lurkers. By most estimates, lurkers make up the vast majority of online communities with most of the user-generated content in those communities coming from a relatively small proportion of members.

While the term may sound pejorative—and it often is—lurking is not always seen as a bad thing. For example, new members of an online community may be encouraged to browse the community’s posts and engagements with them before posting or engaging themselves in order to understand the community’s norms and avoid duplicating content.

Due to their lack of engagement, lurkers are inherently difficult to monitor and understand from an outsider’s perspective. However, community managers may nevertheless use the changing ratio between lurkers and active participants as a metric for measuring a community’s progress.