Constipation is that condition of the digestive system of an individual where the hard feces are difficult to expel. Mostly, it occurs because of excessive water absorption from the food in the colon.
The slower the food moves through the digestive tract, the more water is absorbed by the colon. As a consequence, the feces become dry and hard which ultimately makes the process of emptying the bowels more painful.

Fast facts on constipation
It generally occurs due to excess water absorption from the food
Causes of constipation include physical inactivity, aging, and certain medications
Laxatives should be only used as a last resort
Some cases of constipation can be relieved by certain changes in lifestyle