The initialism AVO stands for "Avoid Verbal Orders" and refers to a written document that provides direction or instruction. I think the meaning is clear from the name... someone was fed up with "he said, she said" conflict.
I think it is used a lot in defense and aerospace, especially NASA. Did NASA come up with it?
I did find that Hughes Aircraft Company used the term in 1987, as documented in a lawsuit against the company:
... she told me to prepare an AVO [avoid verbal orders memorandum] to her with a rationale for the change ...