A lurker is a term used for the homeless on Babylon 5.
Lurkers are mostly human although others have been seen. They began settling on the station as soon as it was opened, beginning simply as people searching for new lives and opportunities. When they did not succeed, they often don't have the money to go back home so they end up moving into the undeveloped parts of Downbelow. There are also those that are destitute because they are on the run from something or someone, like the Psi Corps. Lurkers have hard lives to say the least and as if being poor and homeless wasn't bad enough, they often become victims of the criminal underworld that robs and steals from them. However, there have been situations where they are hired by smugglers etc. to handle illegal cargo.
As these people search for items to trade, sell, and eat they are often subject to numerous hazards. From eating tainted, discarded food to being political targets and bomb victims.