A belt without a buckle, especially if a cord or rope, is called a girdle in various contexts, especially historical ones, where girdles were a very common part of everyday clothing from antiquity until perhaps the 15th century, especially for women. Most girdles were practical pieces of costume to hold other pieces in place, but some were loose and essentially for decoration. Among the elite these might include precious metals and jewels.
Today, girdles are part of Christian liturgical vestments, and the word is used in other contexts, such as American sports (for what is really a kind of underwear).
The girdle as an undergarment or abbreviated corset around the waist is a different, essentially 20th-century, concept, but from around 1895 there was a fashion for "girdles" as a separate section of a fashionable dress, worn just above the waist on top of the main dress. It was typically up to about eight inches high, and often terminated in a "V" shape. It might be the same colour as the main dress or not. It differs from the earlier Swiss waist of the mid-19th century by not having lacing or boning.