Yes, DEPRESSION is a Scrabble word!

Letter values in Scrabble US: D 2, E 1, P 3, R 1, E 1, S 1, S 1, I 1, O 1, N 1.

Is it a valid word?

DEPRESSION is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a mental state characterized by a pessimistic sense of inadequacy and a despondent lack of activity
a long-term economic state characterized by unemployment and low prices and low levels of trade and investment
a sunken or depressed geological formation
sad feelings of gloom and inadequacy
a period during the 1930s when there was a worldwide economic depression and mass unemployment
an air mass of lower pressure; often brings precipitation
a state of depression and anhedonia so severe as to require clinical intervention
a concavity in a surface produced by pressing
angular distance below the horizon (especially of a celestial object)
pushing down

Also: economic crisis, natural depression, great depression, depressive disorder, clinical depression.