The metal cylinder, with three or four lateral slots, designed to hold the Knives of Jointers, Planers, and Molders securely while the rotary action of the assembly flattens, smooths or cuts a profiled pattern on a workpiece. Or, because of the recent appearance of Spiral Cutterheads and Indexable Carbide Spiral Cutterheads, that old-style cutterhead is becoming dated. The cylindrical cutterhead was preceded by the "Square" Cutterhead; see the 2d image below.

cutterhead anatomy
four knife oliver and square cutterhead

One would think that, with its two cutting edges, the auger bit would have preceded the rotary cutterhead of the planer and jointer. Such is not true, though, as the rotary cutter head concept preceded the two-edged auger bit by a century. Samuel Bentham (dates), labeled by some the "father of the modern woodworking machine," is credited with inventing the rotary cutterhead. Impact per Ettema also from Ettema, n. 20 Richards, Treatise, pp. 5-6. also Richards file.