The term depression gets thrown around a lot colloquially. Depression though relates to mental illness as either something psychiatric (where it is as much a medical condition as heart failure (inappropriate pun intended)), or psychological, something more serious that is to do with life and circumstance.
I don't dispute the use of the term, general usage is justified. Medical terms are relevant to how we see the world, and are useful in explaining things analogously. I'm depressed, I've been manic, I just seem to be bipolar, my OCD is playing up, or saying I've got some ADD tendencies makes sense in explaining yourself. It also doesn't detract from the medical definitions because we’re all smart enough to understand the difference.
The only harm is could be in disempowering people when you label yourself or others with a critical definition. Saying you're the kind of person who will never be happy can really keep you miserable. I'm not however advocating telling yourself you're beautiful in the mirror in the morning 10 times, or smiling in the mirror when you’re unhappy because that stuff is actually hokum.
Depression in a less medical more general use, I like to describe like as being; the difference between your perception of what life/the world should be, and what it is.
Take for instance love again. If you believe that at 29 you should happily have a partner and child, and you don't, you can find yourself quite seriously depressed. I've seen something similar in a friend who in all other areas of life was successful; good job with prospects, friends, hobbies, community ... but the singular belief they should be in a relationship was crushing, and influenced their perceptions of everything else.
Love is perhaps one of the biggest causes of depression, especially after a major shift like a break-up or family death. The world no longer has a person, and that can be debilitating. But it can be any singular thing, like my temperament without a morning coffee, or a larger issue like conceptions of reality being shifted.
The hardest part of overcoming depression is that it inherently puts you in an inactive state. And in order to get out of it, you have to be active. That could mean forcing yourself into distraction, or being social when it seems like a the last thing you want.
Beyond that asking for help is even harder if you are already feeling weak and unempowered. Even if you feel a bit selfish, talk to somebody though.
Firstly, you realise everyone has shit wrong and you aren’t alone. Secondly, you actually become closer to people. Thirdly, if somebody realises you’re possibly depressed in the medical sense you could actually take the first steps from there to moving on.
Turning Pro - Steven Pressfield For motivation.
The First 20 Hours - Josh Kaufman For inspiration.
The Secret - Rhonda Byrne For reassurance you're better than the people who believe this shit.
The Alchemist - Paulo Coelho Preachy, but easy reading.
Fear and Trembling - Søren Kierkegaard To remember that people have had fucked issues for thousands of years.
The Myth of Sisyphus - Albert Camus Okay, everything is fucked, we get it. Accept that's the natural state of things. Now what are you going to do about it?
The Acme Novelty Library - Chris Ware A reminder you're young, and accomplishmnets take a life time.
I Hope They Serve Beer In Hell - Tucker Max It's hard to stay truly sad when laughing. Life doesn't have to be serious.