Epistaxis refers to the spontaneous discharge of blood from one or both nostrils or the mixing of nasal discharge with blood.
Epistaxis is usually caused by a violation of a smaller blood vessel or bleeding from a larger area of the mucosa (called suffusion). The bleeding may be caused by different factors:
Often there is no clear cause. This is called idiopathic or recurrent nosebleeds.
Source: Welleschik via wikipedia