meaning - What is "Web Copy" and why does everyone refer to it without an article?

I recently read a blog post that talks about "Web Copy".

I have never heard of this term before, so I did some searching around. I'm still not sure what the meaning of this is.

What bugs me is that everyone who uses it refers to it without the use of an indefinite or definite article before. For example, in the blog post mentioned, the author says "How do you learn to write web copy?" instead of "How do you learn to write a web copy?". Other places use it in this 'proper noun' usage (though it isn't capitalized).

Can someone please define the term and explain why there is no article?