Your nasal septum is that thin wall that you see in your nose that separates your nostrils. A deviated septum simply means that this wall is out of line and is blocking off a part of one of your nostrils. While this condition can happen during early fetal development, most cases are often due to some type of nasal trauma.
A deviated septum can cause difficulty breathing, an increased chance of nosebleeds, an awareness of the nasal cycle, or noisier sleep breathing. The severity of these symptoms range in each case, as it all depends on just how off-center the septum is.