tart ring (tahrt ring) noun
Also flan ring. A ring usually made from tinned steel or stainless steel used to form a tart on a sheet pan. Tart rings are typically 5/8-inch to 1 inch in height with rolled edges. They do not have a bottom, as some tart pans do, so they must be used in combination with a flat pan, upon which the bottom of your tart crust will rest. They can be round or other shapes, but are still referred to as rings. They come in all sizes, including small 3- to 4-inch individual sizes, as seen in bottom image. Immediately below you can see what a fruit tart looks like unmolded.
Images: Dédé Wilson