"Millwork" refers to ready-made products for finish construction. They are usually produced by a wood mill, from which comes the name.
Common examples of millwork include doors, door and window casings, trim, baseboards, crown moldings, mantels, columns, ornamental brackets and corbels. Stairway railings are often made up of millwork, such as banisters, balusters and newel posts.
Millwork has traditionally been fashioned from wood, and the vast majority of it still is. But more millwork products are being made of plastics and composite materials.
Millwork is distinguished from lumber, which is wood used as a structural material. In a typical finished room, if it's inside the walls, it's lumber; if it's in view, it's millwork.
"Casework" and "millwork" are sometimes used interchangeably, but casework actually refers to assembled cabinetry or cases. Millwork often goes into the production of casework, but it is not casework in itself.
Millwork is usually sold unfinished, allowing buyers to customize it with paint or stain. Finished millwork, when available, usually comes in only a few variations--white or oak, for example. Custom-finished millwork can be ordered.