My jack is all jacked up

Guitar Lesson

I've got this prob with my electric's cord input jack; I'll just
get a buzzing sound unless I push in the cord and hold it there.
Sometimes if I'm lucky I'll find the spot where it doesn't buzz. but it
always starts up again. I checked the cord and the wires on the guitar
connected to the jack. all are good. Any ideas as to what's wrong?