Kanban is a signalling mechanism that regulates work by limiting how much can be in progress at once. The word means signboard; the signal can be a card, a container, an empty space or a column.
Its defining property is that work moves when the receiving step signals capacity, not when the sending step finishes. Under push, each step produces at its own pace and work piles up wherever the next step is slower. Under pull that accumulation cannot happen, because nothing signals for production into a full queue.
The work-in-progress limit is the mechanism, not a guideline. When a column is full nothing new enters until something leaves, which forces attention onto the bottleneck instead of letting it hide beneath a growing queue. Teams used to starting work freely experience this as obstruction, and the instinctive response — raising the limit — removes the only part that was doing anything.
Originally manufacturing, but the principle transfers directly to any queueing process: support tickets, claims, recruitment, software delivery. A board showing fifty items in progress and enforcing nothing is a status display, not a Kanban system.
