What is it called when a non-verb is used as a verb?

This is in very common use on the internet. I just read this:

"[The] hotel employee walks in, I say "uh, puppy" and she just NOPEd the [heck] out of the room."

This is often done by adding 'd to the word.

Solution 1:

I think the term you are looking for is "verbification":

Verbification, or verbing, is the creation of a verb from a noun, adjective or other word. Verbification is a type of functional shift. It is also a form of derivation, and may involve any of the various derivational processes.

This is a process of conversion of a word to include more word-classes for the lexicon.
This applies to any non-verb, even "proper nouns":

Proper nouns can also be verbed in the English language. "Google" is the name of a popular internet search engine. To google something now means to look it up on the internet, as in "He didn't know the answer, so he googled it."

That's a favourite, "google" is.

Solution 2:

As others have said, "verbification" is common. The highfalutin Greek name of the more general concept of using a word as the "wrong" part of speech is anthimeria.

See also Calvin's opinion on the subject.

Solution 3:

When any lexeme changes its word class without affixation, the process is known as ‘conversion’.

Solution 4:

Verbification, or verbing. See Wikipedia's entry on linguistic conversion.