In a deviated septum the thing that is deviated (basically, not straight) is the nasal septum, the wall of bone and cartilage that runs down the middle of the nose separating it into two nostrils/nasal passages. Most people, in fact, have a modestly deviated septum and as long as there is no blockage this deviation is not necessarily a significant medical concern. The person can breathe and other jobs of the nose such as smelling and hydrating the airflow should work as normal. However, there are side effects of symptoms of a deviated septum that can significantly disrupt one's life.
A deviated septum can be out of alignment to greater and lesser degrees, and this misalignment can be the result of imperfect development or of an impact trauma. It can effect a person's appearance, promote snoring, make it more difficult to breathe in the smaller nostril, encourage sinus infections, and increase the number of nosebleeds.
Treatment: Surgery can repair a deviated septum, but it is not without risks. Nasal strips can open the nostrils wider to promote unobstructed breathing and reduce snoring. A natural degongestant can help reduce breathing difficulties.