Handlebars are the bar at the front of a bicycle or a motorcycle. You hold them and turn them, and that turns the front wheel, so you go left or right. They usually have two sides with grips, and often brakes and a bell, so English nearly always says handlebars, not handlebar. On a bicycle they sit above the front wheel; on a motorcycle they sit in front of you and are often wider. People also talk about a handlebar moustache, which curls out like the ends of old bicycle bars. That is only about the shape.

車把。台灣騎腳踏車常講「龍頭」；騎機車則多講「把手」。