Correction: Freud described depression as anger turned inwards.
Specifically, he described anger at external forces (your mother, etc.) turned inwards. In his view, the only way to get rid of depression would be to allow this anger to express itself against the actual external force. This is very, very far away from the majority view of modern psychology (which has dismissed the vast majority of Freudian thought), but I still hear it repeated all the damn time.
The reason I think it's important to correct it is that therapies based on Freud's notion of depression not only aren't helpful, they in many cases made a person worse. It turns out, getting a person to focus on all the things that should make them angry in their life is, in fact, not helpful for their general mental health.
It is true that depressives tend to think a lot of shitty things about themselves. More successful cognitive behavioral therapy (which has been clinically proven to be as helpful as antidepressants in treating non-severe depression), tries to train people to think of alternatives to those shitty thoughts without necessarily saying which one alternative is right. Turns out, getting in the habit of thinking not just the worse thing possible is actually quite helpful. It gets you out of the rut your in.