To describe the end of a way.
Use the noexit=yes tag at the end of a highway=* to indicate that there no possibility to travel further by any transport mode along a formal path or route.
This tag is mainly useful where a road or path ends close to another way but where it isn't possible to get through due to a barrier or other obstruction which may otherwise look like a mistake for a connection to the nearby road. It helps other mappers and quality-check programs to understand the situation correctly.
This tag should not be used where the way is only it is a dead-end for one transport mode, but where other modes can continue. By way of example don't use it at the end of a motorised road where a footpath continues. Where a road ends in a turning circle, use highway=turning_circle instead.
If you wish to indicate that a way does continue but that you have been unable to map it for some reason use fixme=continue (or any other text) to show that a way goes further but is not mapped yet. This may often be a very short stub from a road indicating the start of a path or side road.