Thigh-high boots , known also as thigh-length boots or simply thigh boots , are boots that extend above the knees to at least mid-thigh. Other terms for this footwear include over-the-knee boots abbreviated OTK boots; the full term is also used for the 15th century riding boots for men, later adopted by women and, especially when cuffed, pirate boots. Lengths vary from reaching just over the knee to reaching almost to the crotch referred to as crotch boots or crotch-high boots. Thigh boots are made of materials ranging from various leathers to various synthetic materials including vinyl , polyurethane , or latex to various fabrics such as silk or polyester microfiber. Many are constructed with zippers, but some are designed as pull-on boots.
Boot fetishism is a sexual fetish focused on boots. Boots have become the object of sexual attraction amounting to fetishism for some people and they have become a standard accessory in BDSM scenes where leather, latex and PVC boots are favoured and a fashion accessory in music videos. Hermine Hug-Hellmuth described boot fetishism scientifically in Richards in , as Female fetishes and female perversions: Hermine Hug-Hellmuth's "A case of female foot or more properly boot fetishism" reconsidered. Boots were used by S. Rachman as a subject for research on conditioning as a cause for fetishism in the s, making men sexually aroused by seeing pictures of boots,  but the results have been put into question later, as boots already were very much en vogue for sexually attractive women at the time. Unlike shoes, boot styles have often appeared as street wear before they inspire fashion designers.