A unique word or phrase that has been passed down from granfather to grandchild. It often has a humorous twist and is imediately adopted into the child's vocabulary.It is then quoted by said granchild whenever possible and often serves to poke fun at the adult who inadvertantly provided them the opportunity.
Son: "Do you like that red Vette dad?
Dad: "Yahbut, I think ..."
Son: "You said Yahbut dad, that's a Papa-ism"