Hello dear,
if your depression lasts longer than 2 weeks with with few of these symptoms such as
your sad and tearful
your apetite is less or increases than usual
trouble sleeping
your agitated/ restless
losing interest in things you previously liked
gained/lost weight, you have no energy
feeling of worthlessness/trouble concentrating
feeling suicidal

Hi ehra25,
There r verious features mentioned below indicates that person is suffering rom depression...but significant one is these feature significantly affecting ur sociooccupational and if there then acdemic performances and affecting for signiicant period.
Features includes:
Feeling low-sad,hopeless helpless worthless feeling,disturbed sleep and appetite,disinterest in previously interested things,displeasure in previously pleasurable things,thoughts of harming to self,slownees in activity....decreased concentration....etc