A major depressive episode includes symptoms that are severe enough to cause noticeable difficulty in day-to-day activities, such as work, school, social activities or relationships.
An episode includes five or more of these symptoms:

Depressed mood, such as feeling sad, empty, hopeless or tearful (in children and teens, depressed mood can appear as irritability)
Marked loss of interest or feeling no pleasure in all — or almost all — activities
Significant weight loss when not dieting, weight gain, or decrease or increase in appetite (in children, failure to gain weight as expected can be a sign of depression)
Either insomnia or sleeping too much
Either restlessness or slowed behavior
Fatigue or loss of energy
Feelings of worthlessness or excessive or inappropriate guilt
Decreased ability to think or concentrate, or indecisiveness
Thinking about, planning or attempting suicide