What is media and why do artist use certain types of media over others?

Question

The word "media" is simply the plural form of "medium." A medium is simply the particular form or material that an artist chooses to use. For example, oil is one medium for painting; acrylic is another; watercolor is still another. There are many more. Sometimes an artist will work with more than one medium, in which case it's called mixed media.

In sculpture, marble is one medium, while bronze is another, and wood is still another.

Artists' choices are based on lots of things, including what they have had success with, as well as what they'd like to experiment with. There is no one answer to that question.

If you click on the Art link at the left (top of the list) you will find lots of resources to help you find information.

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Writeacher has it exactly. Several of my ex-students classify media as two-dimensional, three-dimensional, multimedia, or graphics. Within each of those broad categories, there are subdivisions: materials used, colors, textures, themes, and motifs.
I am looking at my Dali in front of me (Christopher Columbus discovering the New World)....media includes style also.