Hacking is a mindset.
You can hack everything with the proper mindset. You can hack even your thoughts if you truly believe so. I'd say it's when you learn every detail about something and then using that knowledge to create something new or improved. I can type these words just to type them or I can type them with the proper attitude and knowing that 'exploit' or 'rule' I know how to modify, use or break it. Simple as that. Now you can use that mindset on every thing in your life. Not satisfied with your body? Hack it! Not satisfied with your social skills? Hack them!
Hack to learn, don't learn to hack.
Exactly. If you want to hack someones system or website, don't do it for the hacking itself. Do it for the sake of learning new things, and learning how those things operate. The journey is more important than the destination.
So, what exactly is hacking? I'd say hacking is a lifestyle, a mindset. To overcome every problem e.g. nothing is impossible.
When it comes to these terms, hacking and computers than hacking is an art. You can't be a hacker if you want to just ruin someones system or break in it. If you want to be a hacker you need to know exactly what you're doing, how you're going to do it and the most important thing - why you're doing it in the first place.
Here are a few articles that I'd put into 'introducing' zone. Enjoy learning new things!
cs.berkeley.edu/~bh/hacker.html
catb.org/esr/faqs/hacker-howto.html
en.wikipedia.org/wiki/Hacker
Take a cookie, now introduce yourself and get your exam from the doctor