“Colic” is kind of a catch-all term for fussy babies, typically manifested by increased crying or fussiness. Some babies are more easy to console than others. In any regard, colic can cause significant distress in parents...sometimes even more distress than the infant!
Colic typically occurs at 4-6 weeks of age, nobody seems to know exactly what causes colic, but how do you deal with it? A fussy baby can wreak havoc on your lifestyle. Dr. Harvey Karp's book "The Happiest Baby on the Block" details the 5 "S's" of Swaddling (tightly wrapping) the child, letting the child Suck on a pacifier or breast, making a "Shhh" sound, laying them on their Side (when supervised), and Swinging them in your arms. This seems to help calm most infants with colic. These tips can be found in Dr. Karp's book, which offers tremendous advice for parents.