A collapsible gate, also called a scissor gate, is a folding metal grille made of vertical bars joined together by flat bars crossed in a scissor pattern. When opened it does not go up: it gathers to one side, folding like an accordion, and slides along a track on the floor, at the top or in both places.
You see it on older shops, entrances, shop windows and garage accesses, because it protects without covering everything: you can see through it. It usually locks with a side lock or a padlock.
What fails most is the sliding. If the floor track fills with sand or dirt, the gate jams, one of the flat bars ends up bent and it becomes hard to close fully. Keeping the track clean helps a great deal. If it has bent or will not close, send us a photo: we look at it in roller shutter repair.