The common definition of depression, which may occur in individuals of all genders, ages as well as backgrounds, is a psychological disorder or chaos that affects an individual’s mood changes, public contacts and bodily functions.

Subsequently, depression is a general mental or psychological disorder that presents with low mood, loss of concentration or happiness, feelings of remorse, disturbed sleep or desire for food, and low energy. Moreover, depressive signs and symptoms vary significantly from individual to individual as well as do the reasons.

It influences the way you eat and sleep, the manner you feel about yourself, and the way you think about things or issues. Depression, which is a sort of mental disarray that affects an individual’s frame of mind, triggers changes in thoughts, actions as well as physical well-being.

Depression is a mental disorder that affects many people regardless of age, gender, race, and background. Depression is a mental state characterized by extreme sadness and feeling of loneliness. It greatly affects the life of a person in general because most of the time, it leads to suicide.

According to the World Health Organization:

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Depression is a common mental disorder that presents with depressed mood, loss of interest or pleasure, feelings of guilt or low self-worth, disturbed sleep or appetite, low energy, and poor concentration. These problems can become chronic or recurrent and lead to substantial impairments in an individual's ability to take care of his or her everyday responsibilities. At its worst, depression can lead to suicide, a tragic fatality associated with the loss of about 850 000 lives every year.
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Source: http://www.who.int/mental_health/management/depression/definition/en/

For complete information about depression symptoms, causes, treatment, and information on getting help and coping, the following site may be helpful.

http://www.nimh.nih.gov/health/publications/depression/complete-index.shtml

The exact definition of depression is that it is a prolonged sadness and frustration which manifests itself as a serious mental disorder which significantly impacts a person’s life. It should be viewed as an illness that affects a person physically, mentally and behaviorally. It will dramatically impact the manner in which an individual eats, sleeps, feels about themselves, and the way they view the world around them. Depression is a long-term condition that needs to be treated before it becomes pathological, as it will then become habitual and severely affect a person’s life. Without treatment, depression symptoms can last for weeks, months, or even years. It is advisable to you to research how to diagnose depression, and how to treat depression.

The various other symptoms of depression include unexplained mood swings, excessive tearing or crying, changes in eating or behavioral patterns, loss of weight, increased irritability, issues with concentration, and various physical ailments.

With regards to some of the literature which can help you in your search, there are several books on depression. These books include "Feeling Good: The New Mood Therapy", "Beyond Prozac : Brain-Toxic Lifestyles, Natural Antidotes & New Generation Antidepressants", "Win the Battle: The 3-Step Lifesaving Formula to Conquer Depression and Bipolar Disorder", "An Unquiet Mind", "Growing Up Sad: Childhood Depression and Its Treatment, Help Me", "I'm Sad : Recognizing, Treating, and Preventing Childhood Depression", "The Antidepressant Survival Guide: How to Enhance the Benefits and Beat the Side Effects of Your Medication", "Undoing Depression : What Therapy Doesn't Teach You and Medication Can't Give You", "When Madness Comes Home: Help and Hope for the Children", "Siblings and Partners of the Mentally Ill", and "Remembering Wholeness: A Guidebook for Thriving in the 21st Century", among others.

Pyschology Info Online says:

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Depression is a psychological condition that changes how you think and feel, and also affects your social behavior and sense of physical well-being. We have all felt sad at one time or another, but that is not depression. Sometimes we feel tired from working hard, or discouraged when faced with serious problems. This too, is not depression. These feelings usually pass within a few days or weeks, once we adjust to the stress. But, if these feelings linger, intensify, and begin to interfere with work, school or family responsibilities, it may be depression.
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However, this definition is very broad, since depression falls into several different types, which are themselves very different in their effects and symptoms. WebMD says that depression falls into several categories. There is, for instance, major depression, which is a depressive episode that lasts for more than two weeks and effects a person’s enjoyment in once-loved activities and impairs said person’s ability to function. There is chronic depression, which is less disabling than major depression, but still affects a person’s ability to enjoy life. Additionally, there is atypical depression, which is a sort of functioning depression that usually comes on during teen years; bipolar disorder, where the person’s mood fluctuates from depression to mania; and seasonal depression, where depression is affected and caused by the change in seasons.

The best thing to do if you or a loved one are suffering from depression is to go see a professional, who can give you a better diagnosis. Psychology Today has a great section on their website called “Find a Therapist,” that can help you locate a mental health professional who specializes in the kinds of issues you’re having. It will also tell you if the therapist has a sliding scale for payments, in case you can’t afford the full price.

Best of luck and take good care of yourself.