A sound effect created by Don Martin of Mad Magazine used to indicate the rapid pulling or removal of an object, much like 'Pow" or "Bam" would indicate a punch or hard hit in a Batman comic. Later used numerous times by characters on The Simpsons to indicate quick grabbing of something belonging to others.
"It's mine", said Bart. "No, it's mine", said Lisa. "Yoink!". Now it's mine, said Marge.