According to the Oxford English Dictionary,
Depression is: A mental condition characterized by feelings of severe despondency and dejection,

But for me,
Depression is the sleepless nights,
And the reason I don't get out of bed

Depression is the still unwashed plates
Left by the sink,
The missed calls and the
Voicemails that I never open

Depression is the chipped paintwork,
The shatter glass windows that
I have not got round to fixing

Depression is the skipped meals,
The self-portrait it carves on my wrist,
It controls me like a puppeteer

Depression is the voice telling me
That I am not good enough
Not smart enough,
Not funny enough

The voice telling me this world would be better without me
Telling me I am not wanted,
I am not loved

Depression is the reason I can't treat my friends and family
Like friends and family

Depression is standing on top of the world
And still wanting to jump

Depression is not wanting to die and
Yet still wanting to die

Depression is the hardest battle I've ever fought
And I think I'm losing