Trello is a web-based project management tool that utilizes boards, lists, and cards to organize tasks and projects visually. It allows users to create boards for different projects, add lists to represent steps or stages, and use cards to detail specific tasks, which can be moved between lists. Trello includes features such as drag-and-drop functionality, task assignment, due dates, labels, checklists, and collaboration tools. Users can also integrate Trello with various other services and applications.