Kanban (signboard in Japanese), like Scrum, is one of the agile methodologies. But unlike Scrum, it is a visual workflow management. Besides, Kanban uses a continuous workflow, not sprints. It appeared as a part of Toyota workflow as boards and cards to track the factory production and teams tasks.
Workflow visualizing helps to limit the number of items in process and minimize the chaos. With the help of boards, teams can manage the collective work using WIP limits and tools.
See also Scrumban.