Define Wives Tale Meaning

"Don't swallow gum or it will stay in your stomach for seven years."
"Mom that's an old wives tale"

"Dude I wanna know what sex my baby's gonna be"
"Spin a locket around ur wifes belly, depending on the direction of the circle you might either get a boy or a girl"
"Dude thats an Old Wives Tale, I think Im just goin to use an ultra sound"
"Fu** you smart ass!"

Bobby's Grandma: "Put on your coat or you'll catch pneumonia"
Little Bobby: "Nah ah Grandma. That's an old wives tale. Pneumonia is caused by bacteria."