Tie wire
Soft annealed wire used to tie reinforcing bars together so the assembly holds its position during concrete placement.
What does tie wire mean?
Tie wire carries no design load; its only job is keeping the cage together until the concrete sets. Ties are typically required at a proportion of intersections rather than at every one, and ends are turned inward so they do not project into the cover zone where they would rust and stain. Wire twisters and battery-powered tying tools have largely replaced hand pliers on large jobs.
In practice
Tie ends left sticking toward a formed face produce rust spots on the finished wall a year later.