WooCommerce is a free and open-source e-commerce plugin for WordPress, one of the most widely-used content management systems (CMS) for building websites. It allows website owners to easily set up an online store, list products, manage orders, and accept payments. WooCommerce is highly customizable and offers a range of extensions and add-ons that enable additional functionality, such as shipping and tax calculations, email marketing, and payment gateways for various payment methods including credit cards, bank transfers, and cryptocurrencies.