First of all, what is hacking? Well, quite simply its doing something for the fun of it. It is a little like creating a piece of art, a painting or sculpture. Of course there is no set rules as to what hacking is and isn't - just like with art for example, there are many ways to express an idea to your audience and there is no right or wrong way to achieve that. However, most people equate hacking with finding vulnerabilities in a computer and being able to do something with them. This can be anything from turning the computer on to being able to access the entire database on the computer and potentially steal information out of it ("hacktivism"). While hacking definitely does involve using computers for malicious purposes, hacking also goes way beyond this and includes hobbies such as programming hacks (both in software and virtual scenarios), cracking code or teaching others how to code or hack safely.
Programming/coding Hacks (aka Wreaking Havoc/Bug Zapping): The act of purposely introducing a bug into a piece of software that is intended for use by the general public with the intention for them to discover the problem themselves and hopefully make a bug report to the vendor of the software so that it can be fixed. While programming bugzapping is usually considered a part of white hat hacking by many in the hacker community, some hackers believe that you shouldn't always report bugs found and instead actually fix them for your own amusement. Of course many other hackers enjoy the act of reporting problems they find with source code and having a laugh at the ingeniousness of the person who wrote it!
Cracking Code: The process of working backwards from something, such as a program or file, to obtain a copy of the object code from the original. Usually involves trial and error methods to try and isolate the program and/or file so an attacker can then work down the list of source files they compiled into one big block of code that can execute on the system. Most common methods used are hash collisions and hidden command injection.
Teaching Others How To Hack Safely: A very popular activity amongst many who spend most of their free time learning new skills is teaching others these skills you have acquired. This can include everything from learning how to code basic bash scripts to learning how to navigate around a shell on a system and expose users to risks they aren't aware off. Most commonly taught skills would be web scripting, shell scripting and SQL injection techniques. It is very common for individuals to hone their teaching skills and have dedicated forums where they meet online regularly and teach others about specific subjects of interest.