Question

is "every bit" a slang term?

Answer 1

Not exactly. It is a colloquialism for the word all. You would not use it in an academic paper. Simply use the word all.

Answer 2

I'd call it "colloquial" (we use it in conversation), not slang. So if I use it in writing, it makes the writing sound a bit more conversational.

Answer 3

It is certainly okay to use in informal writing, but not formal or academic documents.