radiation pressure: the minute pressure exerted on a surface normal to the direction of propagation of a wave
pressure: the force applied to a unit area of surface; measured in pascals (SI unit) or in dynes (cgs unit)
ovulation method of family planning: natural family planning in which the fertile period is inferred from changes in the character and quantity of cervical mucus; ovulation is marked by an increase in mucus that becomes sticky and then clearer and slippery