Bell-bottoms are trousers that become wider from the knees downward. Related styles include flare, loon pants and boot-cut/leg trousers. Hip-huggers are bell-bottomed, flare, or boot-cut pants that are fitted tightly around the hips and thighs.

Bell-bottoms' precise origins are uncertain. In the early 19th century, very wide trousers ending in a bell began to be worn in the U.S. Navy; however, at this time clothing varied from ship to ship. In one of the first recorded descriptions of sailors' uniforms, Commodore Stephen Decatur wrote in 1813 that the men on the frigates United States and Macedonia were wearing "glazed canvas hats with stiff brims, decked with streamers of ribbon, blue jackets buttoned loosely over waistcoats and blue trousers with bell bottoms." Though the British Royal Navy usually was the leader in nautical fashion, bell-bottoms did not become regulation wear for the Royal Navy until the mid-19th century. These "bell-bottoms" were often just very wide-legged trousers, unlike modern versions cut with a distinct bell. While many reasons to explain sailors' wearing of this style have been cited over the years, most theories have little credibility because there is no reliable documentation.