a. As used by drillers, a borehole that is following or has followed a
spiral or corkscrew course; also said of a drill core that has spiral
grooves appearing on its outside surface. Long
b. A drill hole, in rock, that has become three-cornered while drilling.
c. Applied to the three-cornered section of a hole drilled by hand. Though
the bit is supposed to be turned one-eighth after each blow, to insure a
circular hole, the majority of hand-drilled holes are three-cornered.
Dictionary of Mining, Mineral, and Related Terms