Not sure this is a standard term, but it is clear what it means.

I live in an old town with cobbled streets, and one was very unpleasant to walk on for some years because the sand between the cobbles was washed away down the hill when it rained, and elsewhere it simply gets swept away, for instance when snow is swept off the streets.

Indoors, this would be the pointing material or filler between tiles on a floor, which must not crumble and wear away when the floor is swept. (Or disintegrate when people walk on it.)

I don´t think it is more complicated than that.