Definition:
The piece of work represented on a Kanban board move seamlessly from one process step to another, until the work is done. Visualizing work on a Kanban board does help enable better flow.
Sometimes unforeseen internal or external factors get in the way of progress. These factors are called blockers, because they block a card from being able to move forward in your process. Kanban do a good job of visualising blocked work. A common practice is to throw the blocker sticker away once the work has been unblocked. I always get teams to keep the blockers so they can review them for patterns or common sources of blockage at retrospectives.
The piece of work represented on a Kanban board is to move it seamlessly from one process step to another, until the work is done.Visualizing work on a Kanban board does help enable better flow. Sometimes unforeseen internal or external factors get in the way of progress. These factors which blocks the are called blockers, because they block a card from being able to move forward in your process.
Further Reading:
Book: Kanban: Successful Evolutionary Change for Your Technology Business by David J Anderson
Kanban from the Inside by Mike Burrows