I don't know where this goes, so I will post it in here.
A white hat hacker is an ethical hacker or computer security expert who specializes in testing the strength in systems. Some methods of penetration are DoS attacks, social engineering tactics, hacking tools like Metasploit and exploitation of vulnerabilities.
A gray hat hacker is a skill hacker who does both white and black hacker actions. Some things they do are illegal and others are good to society. Grey hat hackers engage in security research, does not support full disclosure of vulnerabilities and will usually report the vulnerabilities to the site administrator. Grey hat hackers do not hack for personal reasons but to help achieve better security.
A black hat hacker is a person who cracks or breaks into a computer network or system with the intent of malicious things. Black hat hackers take advantage of exploits and will destroy files and steal data. Black hat hackers will also make the exploit known to everybody else except the victim. The reason for the name of black hat is because in the old Western movies the bad guys always wore black hats.
I hope this summary helped clear up some terms that are commonly heard in communities.