Jack Frost, in nursery lore, the personification of the frost. Jack Frost is a mischievous boy who unexpectedly bites children's noses, pinches their cheeks, and makes their fingers tingle. Jack Frost paints the window panes with beautiful pictures, he freezes the lakes and rivers, and will often break a water pitcher or a glass if it is left where he can get at it. In winter Jack bursts the hard shells of buried nuts, so that the green leaves can peep forth.