Pastel paintings are traditionally framed behind glass with a raised mat.  Glass protects the delicate pastel surface and the raised mat allows any loose pastel particles to fall behind rather atop the mat. 

A "glassless" pastel painting is one which may be framed without a mat and glass, similar to a painting of oil or acrylic hanging bare on the wall.  The major benefits of a glassless pastel include avoiding the typical glare of the glass, the cumbersome nature of shipping and handling the paintings, and the expense of the framing.

The enamel-like surface of a glassless pastel (the following have been painted on treated oak plywood) allows the pure colors of pastel to shine through.