The term 'Brief Swimming Costume' is a type of swimwear that is typically referred to as Speedos, which is a brand name. Speedos are a type of swimsuit that covers the body from the waist to the upper thigh, and are usually made of a lightweight material such as Lycra or nylon. They are designed to be comfortable and provide minimal resistance when swimming. Speedos are popular among competitive swimmers and athletes, as well as recreational swimmers.