Medium can refer to both to the type of art (e.g. painting, sculpture, printmaking), as well as the materials an artwork is made from.
In relation to art this term has two principal overlapping, even slightly confusing meanings. Painting, sculpture, drawing, printmaking, are all media of art in the sense of a type of art: however, the term can also refer to the materials a work is made from
For example a sculpture in the medium of bronze or marble; a painting in the medium of oil paint on canvas, or watercolour on paper; a drawing in the medium of pencil or crayon; a print in the medium of etching or lithography.
In modern art new media in both senses have appeared. First of all, modern artists, from Pablo Picasso and Marcel Duchamp on, have established that art can be made of absolutely any material, so the media of modern art, in that sense, have ranged from found or appropriated objects and materials of all kinds, to the artist’s own bodily excretions and the body itself. Many modern works are made from a variety of such things and the term mixed media has had to be coined to take account of this.
This expansion of media, in the sense of materials, has given rise to new media in the overarching sense of a type of art. For example, assemblage, installation and performance are all three-dimensional art forms sufficiently distinct from traditional sculpture to become considered new media in themselves. In the case of the first two the medium from which they are usually made is a variety of materials, that is, mixed media. Performance art uses the artist’s own body as the material or medium.
Finally, in a third meaning, the term medium also refers to the liquid in which the pigment is suspended to make paint. So the medium of the medium of oil paint is linseed oil.