Muntins

Merriam-Webster's entry is one line: “a strip separating panes of glass in a sash.” The dictionary sense is about what the strip does, which is separate panes, and it says nothing about whether those panes are separate pieces of glass. That question belongs to the construction, and a maker answers it below.

A muntin works inside a sash, among the panes it divides. Two other words name glass placed around a window rather than divided within it: a transom, which Cambridge Dictionary ties to a window or door, and a clerestory, which it defines by height on a wall. Each has its own entry.

Cardinal Glass Industries describes both constructions in its glossary entry on simulated divided lites. Traditional divided lites come in by comparison, as the version “where each section is a separate piece of glass held together by a grid of muntins.” In that construction every small pane is its own piece of glass.

Simulated divided lites, in Cardinal's words, are “a type of window design that replicates the appearance of traditional multi-pane windows using a single pane of glass with applied external bars.” The bars, it says, “are typically made of wood, vinyl, or aluminum, and are adhered to the interior and exterior surfaces of the window glass, creating the illusion of separate panes of glass.” One pane of glass runs under the bars on both faces.

No source read for this page gives a cleaning instruction for grids or bars. The National Glass Association's wash method, a soak with clean water and a mild, non-abrasive cleaning solution that is then removed with a squeegee, is written for glass and mentions neither; it is set out in the published window cleaning method. What has to be known about a pane before any method starts is covered in why the pane will not tell you what it is.