A piece is a work of art.

Essentially, a piece of art, an art piece, or an art object is an artistic creation of inestimable value. With the exception for "work of art", which may be used for any work regarded as art,  including works from music and literature, the term “art piece” or “piece of art” principally applies to tangible forms of visual art. For example:

A work of fine art: a sculpture or painting

A work of conceptual art or installation art

An enduring and iconic film or photograph

A fine work of architecture or landscape design

An object designed specifically for its aesthetic appeal: a piece of jewelry.

An object designed for both aesthetic appeal and functional purpose: an interior design piece

A production of live performance, for example: ballet, opera, theater, musical concert, performance art