A lurker is someone who watches or reads what others are doing without participating themselves. The term is most commonly used online, where lurkers visit forums, social media sites, or gaming communities to see what people are posting and discussing but never comment, post, or join in. They're like the person who stands quietly at the edge of a group conversation at recess, listening but never speaking up.

Lurking isn't necessarily bad. Many people lurk when they first join a new online community because they want to understand how things work before jumping in. Someone might lurk in a chess forum to learn strategies, or lurk in a crafting group to see what projects others are making. Some people simply prefer to observe rather than participate, enjoying the content without feeling the need to add their own voice.

The word can also describe someone who hangs around a place without a clear purpose, often in a way that makes others uncomfortable. If someone is lurking outside a building or in a dark hallway, it suggests they're lingering there in a suspicious or creepy way, though this meaning is less common than the online meaning.