Answer:
It can be used as a noun meaning "An intellectually pretentious person; a poseur; false, fake" or as an adjective meaning "1. being other than what is apparent, a sham, 2. insincere, or 3. spurious" (it can also be the more common definition of a prefix meaning that it's a fake of the word it's attached to, e.g. pseudonym or pseudoscience)
A sentence using the noun definition might be, "They want to look smart, but they're really just pseudos." (i.e. they're fakers)