I have to laugh on this one. The reason all of you expert quilters have never heard the term sub-cut is you no longer have to read the directions! You girls just grab some fabric, start sewing and a quilt pops out of your machine!
I've seen several strip piecing patterns that use the term sub-cut. Cut these strips, sew together, sub-cut at this size. Maybe newer quilt designers have to make up new terminology so the pattern can be "theirs".