Closed loop

Closed loop or closed-loop may refer to:

Mathematics

 * Loop (topology)
 * Closed curve

Technology

 * A closed feedback loop:
 * Closed-loop transfer function
 * Electronic feedback loop
 * PID controller
 * Closed ecological system
 * Closed-loop communication
 * Ecological sanitation systems or ecosan

Other uses

 * Circular economy, with materials recycled
 * Closed time loop, a paradox of time travel
 * Knot loop, in a knot