Medium describes a construction
Mixed media means that more than one material or process is structurally important to the work. It may combine paint with paper, fabric, photography, found objects, stitching, wax, metal, or digital output.
The term is broad, so a good artwork record names the actual materials. This helps a collector understand texture, fragility, weight, and how the piece should be framed or displayed.
Care follows the most sensitive material
A work containing paper and oil paint should be protected according to the paper, even if paint dominates visually. Avoid direct sun, rapid humidity changes, and contact with glazing unless the mounting method is designed for it.
Dimensional surfaces should not be compressed under a mat. Ask whether a shadowbox, spacer, sealed backing, or open presentation is appropriate before framing.