Nicknames allow you to change your display name on the server. They appear anywhere your username would appear while you're online. Nicknames must be between 3-14 characters and can be changed at max once every 7 days.
Your nickname must be a real nickname you associate with, containing no strong language or references to sensitive or offensive topics, and abides by the server rules.
In the tablist, your real username will be right-aligned for players reference. Players may also use the /realname <nickname> command to view the username behind a nickname.