Final set
The point at which concrete has hardened enough to resist penetration and begins developing measurable strength. Finishing must be complete before this.
What does final set mean?
Final set does not mean the concrete is strong, only that it is no longer plastic. Sawing control joints becomes possible shortly after, and there is a window in which cutting is late enough not to ravel the surface but early enough to precede random cracking. Strength gain accelerates from this point as hydration continues.
In practice
The saw crew's timing is dictated by this transition, and arriving a few hours late is a common cause of cracks that beat the joints.