The way that I explain it in the classroom is that CONTENT is first physically everything that is in a work of art – all materials, all color, form, value, relationships, contrasts, composition and any subject matter.  It is what the work has in it physically and design wise – what it contains (in one of the usual meanings of the word content).  Then the total content or contents of a work of art (or anything that is in a state of becoming a work of art) – all of it together – makes the MEANING – which is called the CONTENT.  So, here the content of a work of art means the meaning of a work of art.

An older printed dictionary says: (noun) 1. Often contents. Something contained in a receptacle.  2. Often contents. The subject matter of a written work.  3. The meaning or significance of a literary or artistic work. 4.  The proportion of a specified substance. 

BEWARE: The dictionary on my computer only talks about it as an adjective: “she had to be content;” a verb: “she was able to content herself;” and finally the only mention of content as a noun is something similar to this usage: “everyone could paint to their heart’s content.”  So on my computer’s built in dictionary, there is no mention of CONTENT as a noun that means the significance or MEANING of an artistic work.  But that is what content means in art language and also in everyday language that might not be used by everybody.

I checked Wikipedia and had to search for “content art” to get any art related content to come up on the word content.  “Form and content” came up saying this: “In art and art criticism, form and content are considered distinct aspects of a work of art.  The term form refers to the work’s style, techniques and media used, and how the elements of design are implemented.  Content, on the other hand, refers to a work’s essence, or what is being depicted.”