Mood is a state of mind where an emotion predominates (anxious mood, bad mood or good mood). An emotion is a general feeling that colours behaviour and the reading of the world around the individual (anger, sadness, joy, etc.) in a sustained way.
Depression is a period of time (typically at least two weeks) when a person feels sad or experiences a marked decrease in interest in activities of daily living on an almost constant basis.
Other symptoms may include weight loss or gain, insomnia or hypersomnia, psychomotor slowing or agitation, fatigue, feelings of worthlessness or guilt, loss of concentration, recurring thoughts of death.
Bipolar disorder usually refers to the presence of periods of depression and periods of mania (formerly manic-depressive disorder). The manic phases manifest themselves by an increase in self-esteem or ideas of grandeur, a reduction in the need for sleep, a constant need to talk, a great distractibility or an excessive involvement in certain activities (shopping, sexual behaviour, etc.).