The phrase mechanic arts is an obsolete and archaic term. In the 19th century, it referred to the fields now known as engineering. It was apparently an attempt to distinguish the engineering fields, in the sense that they are creative and artistic endeavors (but ones that strongly rely on science), from other less scientific fields like the performing arts and the fine arts. A related phrase, "useful arts," probably encompassed the mechanic arts as well as craftsmanship in general.
The most famous usage of "mechanic arts" (and the one in which it is most commonly encountered today) is in the Morrill Land-Grant Colleges Act.
