Hole

A hole is an empty island inside a filled outline, a yard inside a fence, stored as a loop that does not receive material.

Those rings show up as a metal plane with a cutout for a via farm, as a photomask opening on a dark field, and as vents in a MEMS diaphragm. Some files store the hole as a second loop on the same polygon. Others store a positive shape and a separate negative shape that has to be subtracted. If the tool does not understand the hole, it fills the courtyard and the print is a blob. A wide ring might use an outer loop 20 micrometers on a side and an inner loop of 8 micrometers, with material only in the band between them.

The gold shape is filled. The white window inside it is empty and closed all the way around.

Making the window is often a Boolean NOT. Merge can build the same kind of hole when outlines surround a void. A via cut is a hole in insulator once it reaches the factory, but in the file it is usually a solid shape on a cut layer, not a hole punched in the metal polygon. An inner loop drawn with the opposite winding becomes a filled island instead of a window. Check the fill on screen before trusting the file.

The articles holes in polygons, polygons, the real workhorse, and Boolean AND, OR, NOT stay with that inner loop.