Old Master

This is a description or name applied to any painting from an known painter in Europe before “about 1800,” according to Wikipedia.

Merriam-Webster says:

a work of art by an established master and especially by any of the distinguished painters of the 16th, 17th, or early 18th century

But what’s an “established master” or a “distinguished painter”?

The Art Story says:

The term Old Master is used to identify an eminent European artist from the approximate period 1300 to 1800 and includes artists from the Early Renaissance through to the Romantic movement

They go to define the category a little more:

Originally a master artist or craftsman was an individual who had been fully trained in the guild system, and had progressed to working independently, often taking on pupils of their own. This differs from the modern iteration of the term in which artists worked outside of the guilds or in other, more modern, contexts (for example, Paul Cézanne) can also be classed as Old Masters (or sometimes referred to as “Modern Masters”).