Wiktionary
n. A condition in which an otherwise healthy baby cries or screams frequently and for extended periods without any discernible reason.
Wikipedia
Baby colic (also known as infantile colic) is defined as episodes of crying for more than three hours a day for more than three days a week for three weeks in an otherwise healthy child between the ages of two weeks and four months. Colic typically does not result in long term problems. Crying associated with a baby's colic can cause relationship stress, breastfeeding failure, depression following delivery, excess visits to the doctor, and child abuse, such as shaken baby syndrome.
The cause of colic is generally unknown. Some believe it is due to gastrointestinal discomfort like intestinal cramping. Fewer than 5% of infants with excess crying have an underlying organic disease.
Treatment is generally conservative, with little to no role for either medications or alternative therapies. It often disappears when the baby is three to four months old, but can last up to one year. It is present in 5–25% of infants.