Poshmark is a social marketplace that allows users to buy and sell new and secondhand fashion items, including clothing and accessories. The platform operates on a commission-based model, charging a flat fee for sales under $15 and a percentage for higher sales. Poshmark stands out by engaging a community of users and recently introduced a program for large brands to sell on its platform, enhancing product variety. The company's goal is to foster a vibrant marketplace that promotes sustainable fashion practices.