Dowel bar
A smooth bar crossing a joint that transfers load between adjacent slabs while still allowing them to move apart as they shrink.
What does dowel bar mean?
Dowels are deliberately smooth and often coated or greased on one side so the joint can open without restraint while still preventing vertical offset between panels. Deformed rebar used in this role locks the joint, defeats its purpose, and causes random cracking. Alignment matters: dowels installed out of parallel restrain movement and crack the slab.
In practice
Dowels are what keep two sides of a driveway or pavement joint level with each other under a truck wheel instead of stepping apart.