Definition: Hacking is an attempt to exploit a computer system or a private network inside a computer. Simply put, it is the unauthorised access to or control over computer network security systems for some illicit purpose.
Description: To better describe hacking, one needs to first understand hackers. One can easily assume them to be intelligent and highly skilled in computers. In fact, breaking a security system requires more intelligence and expertise than actually creating one. There are no hard and fast rules whereby we can categorize hackers into neat compartments. However, in general computer parlance, we call them white hats, black hats and grey hats.
White hat professionals hack to check their own security systems to make it more hack-proof. In most cases, they are part of the same organisation.
Black hat hackers hack to take control over the system for personal gains. They can destroy, steal or even prevent authorized users from accessing the system. They do this by finding loopholes and weaknesses in the system. Some computer experts call them crackers instead of hackers.
Grey hat hackers comprise curious people who have just about enough computer language skills to enable them to hack a system to locate potential loopholes in the network security system. Grey hats differ from black hats in the sense that the former notify the admin of the network system about the weaknesses discovered in the system, whereas the latter is only looking for personal gains. All kinds of hacking are considered illegal barring the work done by white hat hackers.