Even “minor” depression-states that do not meet diagnostic criteria for a major depressive episode (see below) can cause significant impairment in daily life.  Note that depression is the number one-ranked disease worldwide in females aged 5 and older, and the leading cause of hardships and losses experienced as a result of disease, a measure called disease burden. 
The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) is the standard classification of mental disorders used by mental health professionals in North America. The DSM-5 outlines the following criterion to make a diagnosis of depression:
The individual must be experiencing five or more symptoms during the same 2-week period and at least one of the symptoms should be either (1) depressed mood or (2) loss of interest or pleasure.
- Depressed mood most of the day, nearly every day.
- Markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day.
- Significant weight loss when not dieting or weight gain, or decrease or increase in appetite nearly every day.
- A slowing down of thought and a reduction of physical movement (observable by others, not merely subjective feelings of restlessness or being slowed down).
- Fatigue or loss of energy nearly every day.
- Feelings of worthlessness or excessive or inappropriate guilt nearly every day.
- Diminished ability to think or concentrate, or indecisiveness, nearly every day.
- Recurrent thoughts of death, recurrent suicidal ideation* without a specific plan, or a suicide attempt or a specific plan for committing suicide.
*also known as suicidal thoughts or ideas. This term describes a range of thinking, wishing, and preoccupation with death and suicide.