The channel name is a unique identifier of your channel on this and all the other instances. It's as unique as an email address, which makes it easy for other people to interact with it.
The username is a unique identifier of your account on this and all the other instances. It's as unique as an email address, which makes it easy for other people to interact with it.
I am at least 16 years old and agree to the <x id="START_LINK"/>Terms<x id="CLOSE_LINK"/><x id="START_TAG_NG_CONTAINER"/> and to the <x id="START_LINK_1"/>Code of Conduct<x id="CLOSE_LINK"/><x id="CLOSE_TAG_NG_CONTAINER"/> of this instance