Definition - What does Transpiration mean?
Transpiration is a process by which water is transported through a plant from it's roots to tiny pores on the underside of it's leaves where it evaporates into the atmosphere by changing into water vapour. Transpiration is, in essence, the evaporation of water from the leaves of plants. Transpiration also includes guttation, which is where water is lost from leaves or stems in liquid form.
Safeopedia explains Transpiration
Transpiration is an invisible process, as water vapor cannot be seen due to the small size of water particles, much like sweating. However, a plant may give off many times its own body weight in a single growth season. Studies show that around 10% of the moisture in our atmosphere comes from transpiration. Temperature, humidity, wind, soil moisture, and the type of plant all influence the rate of transpiration.