Conversion: the process of changing the function of a word, such as a noun to a verb, as a way of forming new words, also known as “category change” or “functional shift”.
A change in the function of a word, as for example when a noun comes to be used as a verb (without any reduction), is generally known as conversion.
Other labels for this very common process are “category change” and “functional shift.”
The conversion can involve verbs becoming nouns, with guess, must and spy as the sources of a guess, a must and a spy.
Phrasal verbs (to print out, to take over) also become nouns (a printout, a takeover).
One complex verb combination (want to be) has become a new noun, as in He isn’t in the group, he’s just a wannabe.