Check this out
INA: ACT 203 - ALLOCATION OF IMMIGRANT VISAS
(a) Preference Allocation for Family-Sponsored Immigrants.
(b) Preference Allocation for Employment-Based Immigrants.
(3) Skilled workers, professionals, and other workers
(i) Skilled workers. - Qualified immigrants who are
capable, at the time of petitioning for
classification under this paragraph, of
performing skilled labor (requiring at least 2
years training or experience), not of
a temporary or seasonal nature, for which
qualified workers are not available in the
United States.
(ii) Professionals. - Qualified immigrants who hold
baccalaureate degrees and who are members of
the professions.
(iii) Other workers. - Other qualified immigrants who
are capable, at the time of petitioning for
classification under this paragraph, of
performing unskilled labor, not of a temporary
or seasonal nature, for which qualified workers
are not available in the United States.