There is of course the dictionary definition "the act or an instance of taking one's own life voluntarily and intentionally - but I find that leaves out the core of the concept. I heard a comedian (possibly Marc Maron) say once "I like to think about committing suicide. Not because I want to but because it's relaxing". He's not being cavalier - it's just honesty. Suicide is about one thing - control.
Human nature wants to feel in control of our life. Most of modern society is built upon strategies for feeling in control of your own life whether it be through financial or education investments, insurance, "having a plan", etc. The idea is to make as much distance between yourself and your worst fears because you don't think you could handle life if they came to pass. It's rooted in a lack of confidence in your ability to survive alone because you aren't good enough for yourself and need someone else's feedback. What would you do if you one day woke up and discovered yourself alone on the planet? Would the things that drove you before still be the same? I've found it helpful to put myself in these and other hypothetical situations to get to a point of understanding that I don't have to analyze them all anymore. All the analysis told me was that I could choose to do anything I wanted to but it's my motivation that was all that might change.
People who keep suicide in their rolodex of control strategies are doing so because it helps them feel that no matter what happens they have a trump card. It's really an attempt to tell life to "go fuck itself" because you had the final say. Those who maintain the card and finally reach for it have ultimately believed that it is their last option - last option that is before they have to face the fact that they are what they feared. Bankers who commit suicide in economic downturns can't bear the thought of losing all that they have put their self worth into - i.e. being a "failure". There is of course the matter of those choosing to end their lives to escape what they believe is about to befall them - capture by the enemy, indictment by the SEC, serving time in prison, living in poverty the rest of your life, to name a few.
Suicide is also attributed to careers. "She just committed career suicide publishing that article..." Sometimes people want to walk away from a situation but feel stuck for due to self doubt. The individual knows there will be societal pressure from a number of directions and it's exhausting to weather. Here is a sample - "You quit your job? Whatever are you going to do? This is a terrible economy to be job hunting in. Hope you've got a good plan worked out because I wouldn't want to be in your shoes." Their lack of personal confidence would be projected on you and you doubt yourself even more. Eventually there has to be a reckoning and if not handled properly will result in an extreme action to make sure you once and for all decide. The anger has helped you work up the courage to move on but it's also put you a little over the top because you aren't 100% sure in your decision but you are tired of wavering. It's the equivalent of the generals that supposedly burnt their ships upon on the enemy's shore to give their men no option but victory.
If you are contemplating suicide of any kind it's time to realize there are always options and are no matter what the environment, you are alway in control of your feelings and thoughts. If you just think about it for a second and stop blaming other people you'll realize it's true - you have that power. For all the love you feel lacking towards you in the world, attaining it will never overcome the lack of love you have towards yourself. When you don't love yourself, true love can even be perceived as something twisted because you believe it's what you deserve. Are you trying to "fix yourself" because you feel like there is a better state to be? Or are you just allowing yourself to grow?
A young adult tree blaming itself for growing in a funky shape due to being wrapped around a form as a sapling would be absurd. It could expend energy trying to "make itself normal" upon leaving the nursery trying to grow like the trees in it's new environment, or it could get on with growing. The state you are in when you realize being you is okay and take hold of the power to grow - that is where you start accepting yourself and actually living life. Each day consciously making choices and growing sounds a lot better than swelling into a gnarled blob of branches twisted in on themselves trying to hide or rewrite the past. I heard yesterday that the Chinese don't become angry or fret when an ancient family heirloom such as a porcelain bowl is accidentally broken. Instead they use gold glue to put all the pieces back together (if possible) or make something new out of it entirely. Sometimes life smashes you in the face because it sees what you could be with a few pieces rearranged.