Minecraft wiki entry for tickingarea, associated text: To define a rectangular ticking area covering the rectangle area from (280, 72, 105) to (328, 78, 130), enter either /tickingarea add 280 0 105 328 0 130 or /tickingarea add 280 0 130 328 0 105.
To define a circular ticking area named "Homebase" centered on the chunk you're currently in and extending 2 chunks in every direction, enter /tickingarea add circle ~ ~ ~ 2 Homebase.
To remove the ticking area named "world spawn", enter /tickingarea remove "world spawn".
To remove all ticking areas that contain the block at coordinates (-200, 72, 1000), enter /tickingarea remove -200 72 1000.
To list all ticking areas defined in all dimensions enter: /tickingarea list all-dimensions