Based on the Latin origin of the word, they are birds that live in the silt or mud. That is more or less the case, as they live in a wide variety of wetlands -from the coast to the inland region- and feed on small organisms they find in this type of environment.
In the strict sense they are birds of the order Charadriiformes. All have in common more or less long and highly sensitive beaks to catch and capture small organisms in the silt, sand, wet meadows, etc. Waders include curlews, godwits, dunlins, oystercatchers, etc. Virtually all are migratory and make large displacements between distant places. The record for the longest flight without stopping is held by the bar-tailed godwit, which is capable of flying 11,000 km from Alaska to New Zealand.