Waterproofing protects you from the elements. It is stated in Hydrostatic Head. A garment is classed as waterproof from 1.5K HH. 20K HH = 20,000 mm water column, i.e. a water resistance with a pressure of 2 bar/44 p.s.i.
Breathability is the rate at which perspiration can escape to the outside. This is a highly important element in performance clothing. 25K = 25Kg/m2/24h. So 25 litres of perspiration can pass through 1m2 of the fabric in 24 hours. For comparison, the human body normally releases approximately 6.3L/m2/24h.