Rising damp is a form of dampness that occurs, particularly in older buildings, when groundwater rises up through walls, floors and masonry via capillary action, which is the ability of a liquid to flow in narrow spaces in opposition to gravity. In simple terms, the water rises up the wall of a building in the same way that oil rises up through the wick of a lamp using small continuous pores in a material. Bricks and mortar can be very porous and contain many fine capillaries, through which water can rise.
Bare in mind that Penetrating damp and not Rising damp is the most common form of dampness in buildings