What is the difference bewteen the "writing" word and "speaking" word?

Question

I am writing a paper for a class and we were instructed to use writing words and not speaking words, what is the difference?

Answer 1

Your teacher evidently means for you to use formal English rather than informal or colloquial--no contractions or slang, to begin with. However, "formal" doesn't mean stilted. You don't need to use long words if short (but standard) ones will do, or look up fancy synonyms.

Answer 2

The only person who can truly answer this is the instructor of the course you are taking. They must have mentioned examples of their written word versus spoken word idiom that they clearly invented themselves.

Off the top of my head, I would suggest :
Avoid contractions
Use advanced descriptors rather than simple adjectives
Enumerate using bullets or numbered lists
Encourage the use of metaphors rather than similes
Use strict, proper grammar
Properly cite sources and attribute quotations
Avoid misplaced prepositions, such as ending sentences with the word "with"

Answer 3

Writing words is where you have to correctly write it in terms of spelling, and grammar.
Speaking words is how you speak. This includes "like," "yo," and other slang words.