Fritting as applied to Chinese porcelain is a burst glaze bubble; a glaze loss, which ideally just exposes the undamaged surface of the porcelain body. It occurs at rims and protruding parts of the porcelain piece and is technically caused by the glaze not having mixed with the porcelain body. Frits seems either to have burst open by themselves at the time of firing or to have been cracked open by a soft impact, which would not otherwise have damaged the porcelain.
Fritting are common on porcelain from the late Ming period and rarely occurs at all after the mid 18th century. The difference between a frit and a chip is that a frit is glaze only. If there is a loss of porcelain body too, we have a "chip" instead.
Fritting is usually explained as caused by the glaze not chemically fitting the porcelain body. However, in his letter of 1712 the Jesuit missionary Pere d'Entrecolles writing about the porcelain industry from Jingdezhen, mention this kind of fritting, and explaines that it was caused by the potters touching the edges of the unfired porcelain with their hands.
In either case, from around the mid 17th century this problem appears to have been dealt with by - obviously - 'not touching the edges', but also by applying a brown dressing to the outer rim of the porcelain pieces.