Word economy is saying what you need to say in the least amount of words as possible.
In school we are encouraged to expand the word count of our essays. For some reason the education system thinks there's something to learn from writing a 5000 word essay within which most of the words are redundant.
A more economical way to phrase that would be:
School teaches us to use heaps of words. The education system thinks you can learn from using thousands of them.
I turned 38 words into 20. As you can see it's possible to omit words and say what you need to. The risk, however, is that you can lose some emotion and colour provided by the additional words, so I wouldn't recommend slashing words from artistic pieces.
Word economy also touches on repetition - or the lack of. Since you've already made a point, there's no need to say it again.
Sometimes you will find that rephrasing your text will cull words.
I've been using word economy to improve my writing throughout my career. See some of my work here. I can help you improve your writing (or write for you) if you contact me for freelance work here.