Crinolines are a type of underskirt that gained popularity in the mid-19th century. They are typically made of stiff fabric or horsehair to create a bell-shaped silhouette. Crinolines are also known as hoopskirts, petticoats, or underskirts. The term "hoopskirt" refers to the use of metal or wooden hoops to support the fabric while "petticoat" and "underskirt" are more general terms for any type of skirt worn underneath a dress. Other less common synonyms for crinolines include "cage crinoline," "tournure," and "bustle," which were used to create different types of shapes and silhouettes in women's fashion during the Victorian era.