Chamfer strip is a triangular strip of rigid PVC or Foam PVC , nailed to concrete formwork in various places: outside corners, around window or door openings, at the top of an exposed wall, etc.
Such as the follow :
I will be installing 3/4" chamfer strip for an outside 98 degree corner in a concrete foundation wall. Not the boy band, actually ninety-eight degrees!
For this application, 1 1/2" common nails are sufficient.
Pre-set your nails parallel to one side of the chamfer strip, every 8-12"
Press the chamfer into the corner of the form and carefully nail it off. Because the nails were set parallel to one side, you get a solid bite into one side of the form, rather than the small gap where the two sheets of plywood meet in the corner.
Below is an example of a chamfered concrete corner, which looks tidy and will resist chipping much better than a 90 degree corner.