1962, abbreviation of pornography. Porno (adj.) is attested from 1952.
: The very best porn film ever made/ little prospect of pay-TV turning our homes into porno palaces
nounPornography; a pornographic film, book, etc: the merry world of pimps and porno/ or witness the amount of porn around/ I found out about the porno Rita'd made (first form 1970+, second 1952+)