One-way traffic is traffic

Traffic

Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...

 that moves in a single direction. A one-way street is a street

Street

A street is a paved public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, but is more often paved with a hard, durable...

 either facilitating only one-way traffic, or designed to direct vehicles to move in one direction.
Signs are posted showing which direction the vehicles can move in: commonly an upward arrow, or on a T junction where the main road is one-way, an arrow to the left or right. At the end of the street through which vehicles may not enter, a prohibitory traffic sign

Prohibitory traffic sign

Prohibitory traffic signs are used to prohibit certain types of manoeuvres or some types of traffic.-No entry:No admittance to unauthorised personnel, usually shown as a red circle with a white rectangle across its face.-Speed limits:...

 "Do Not Enter", "Wrong Way", or "No Entry" sign is posted, e.g.