Glaze is very effective for decorating or highlighting grain, especially in large-pored woods such as oak, ash and elm (as shown in the two accompanying pictures).
The term “glaze” refers to a specific product, which is essentially a thickened stain. In addition to a pigment colorant glaze contains a binder (oil, varnish or water-based finish) to bind the colorant to the wood, and thickeners to prevent the glaze from running on vertical surfaces. On flat, horizontal surfaces you could use a pigment stain instead of a glaze.
Glaze, or stain used as a glaze, is always applied over a sealed surface so it doesn’t color the wood. The glaze is also always coated over by at least one coat of finish to keep it from being rubbed off and to bring out its true color. In other words, the glaze is sandwiched between coats of finish.
In the two examples pictured, the wood has been stained, then sealed with the first coat of finish, then glazed with all the excess not lodged in the pores wiped off, then topcoated.
You can also apply glaze over unstained wood, of course, to highlight the grain.