Work, product, production, opus, artifact can all denote a concrete thing that is made or brought into being by the exertion of effort and the exercise of skill.
Work is applied to what comes under this general definition (as something that is manufactured or that is constructed or built) only when used without reference to a particular thing or when used with a possessive or in certain combinations.
Otherwise it is applied to a thing that results from mental labor, especially one involving composition and artistry in execution and specifically called a work of art .
Product (see also PRODUCT 2 ) is applied chiefly to articles of manufacture whether they are made by hand or with the aid of machinery. When product rather than work is used of a poem, novel, statue, or painting, it is often either depreciative in its connotations or definitely noncommittal.
Production is sometimes used where work would be the commoner and more idiomatic term, but it has a formal or slightly bombastic effect except when qualified by a superlative. The term also is specifically applied to a theatrical or similar performance viewed as the work of a producer or director who is responsible for all the details.
Opus is applied chiefly to a musical composition or group of compositions and in this use it is commonly followed by a number designating the order of publication or, sometimes, execution. The term also has some specific application (as to work in mosaic or embroidery) and is used in light criticism of a work of art or literature often with a suggestion of facetious pomposity.
Artifact basically denotes an artificial as distinguished from a natural product; it usually implies human workmanship, largely as a general designation for primitive weapons and implements as well as works of art.