The Nickname is a 9 character long name by which you are addressed on IRC. Nicknames are not "owned", however netiquette requires anyone to repect the right of the one who used a nick first.

A Nickname may consist of the characters a-Z as well as {}[]-|_^\/ and 0-9.
The first character must not be a - or number.

Common names (eg. Jack) make for bad nicknames since they are used by many people. A combination of first- and lastname could be a better idea, or you might like to choose a word that describes yourself.

Choose wisely - you could be using your nick for years to come.