Checkpoint' can be 3 things: 1. predetermined point along a route of march where troops or convoys on the move 'check in' in person at a manned 'control post' and are given further instructions on the route ahead (synonym of "control post" or "control point"); 2. predetermined position along a route where foot, vehicle (or sometimes air) patrols call in their coordinates to headquarters on the radio net, and report on their progress and fulfilment of their mission (synonym of "report point" or "report line"); 3. (the most frequent in a PKO context) a permanent or temporary, self contained, post, e.g. at an entry point to a BZ, where troops or MPs stop vehicular and pedestrian traffic (including civilian) to cheque documents, frisk passengers, search cars etc., in order to stop the smuggling of arms, ammunition and explosives; checkpoints can be static ('fixes') or mobile ('mobiles'); if they are 'closed checkpoints, they are called road blocks.