What Is Constipation? (by webmd.com)

Constipation occurs when bowel movements become difficult or less frequent.

The normal length of time between bowel movements ranges widely from person to person.

Some people have bowel movements three times a day; others, only one or two times a week.

Going longer than three days without a bowel movement is too long.

After three days, the stool or feces become harder and more difficult to pass.

You are considered constipated if you have two or more of the following for at least 3 months:

Straining during a bowel movement more than 25% of the time.

Hard stools more than 25% of the time.

Incomplete evacuation more than 25% of the time.

Two or fewer bowel movements in a week.

Information Source: http://www.webmd.com/digestive-disorders/digestive-diseases-constipation