Hot plunge milling - GIF

[CharlesWaugh]

More accurately: Ramp Entry - Plunge is staright down. As in drill press.
Most endmills are not good at plunging due to zero rim speed at the center (which is why drills are relief-ground to the center-point (hard to do effectively an a flat-face endmill).
Note how the plunge roughing done here is stepping in using just the perimeter of the tool:

(jump to 1:54 to hear him explain plunge roughing)
And, plunge is kinda hard on spindles, who like side loads better'n axial loads.