As far as I know, no statutory definitions are available for the terms unskilled, semiskilled, skilled, and highly skilled. These terms indicate the nature of jobs or work performed by the concerned workmen, mostly with reference to the levels of skill or experience required for their normal performance.
Unskilled Work
Unskilled work is that which requires no special training and involves the performance of simple duties that require the exercise of little or no independent judgment or previous experience, although familiarity with the occupational environment is necessary.
Semiskilled Work
Semiskilled work is one that requires sufficient knowledge of the particular trade in order to do repetitive or simple operations using simple tools and machines.
Skilled Work
Skilled work requires requisite training or sufficient experience enabling the incumbent the capability to work independently and efficiently according to the established standards.
Highly Skilled Work
Highly skilled work is that type of work which requires supervisory ability apart from skill or competence of an extraordinary degree.