This term is defined in ECSS-Q-ST-70-07C as
condition existing in the base laminate of a printed circuit board in the form of discrete white spots or “crosses” below the surface of the base laminate, reflecting a separation of fibres in the glass cloth at the weave intersection

This term is defined in ECSS-Q-ST-70-10C as
condition that occurs in laminated base material in which internal glass fibres are separated from the resin at the weave intersection