Final answer:
Major depressive disorder (MDD) is defined as a mood disorder with persistent low mood and lack of motivation, among other symptoms, lasting for at least two weeks. It's a significant mental health condition that requires treatment to improve.
Step-by-step explanation:
Definition of a Mood Disorder
The term defined as a mood disorder characterized by pervasive low mood, lack of motivation, low energy, and feelings of worthlessness and guilt that last for at least 2 consecutive weeks is known as major depressive disorder (MDD). MDD is a significant mental health condition affecting a sizable percentage of the population globally and entails a severely depressed mood, diminished interest in activities once enjoyed, changes in appetite and sleep, and difficulty in concentrating among other symptoms. It is differentiated from normal sadness or grief by its intensity and duration. The causes of major depression can include both genetic and environmental factors, and treatment options include psychotherapy, medications, and at times, electroconvulsive therapy. Research on the biology of depression has led to various hypotheses, including alterations in neurotransmitter activity such as serotonin, norepinephrine, and dopamine. Antidepressants often target these neurotransmitters to alleviate symptoms.