From AmtWiki

Undeclared is an alternate sign-in option.

Undeclared is not a playable class. It is an alternative usually used by Prime Ministers to track players who signed in before battlegames occur. It has been used by some for new players to give them flexibility in picking their first class, giving them an alternative to 'wasting' credits on a class they wont like. Most lands allow players to move their Undeclared credits to the class of their choice upon request, but this is usually limited to prevent abuse and ensure players actually play a class to gain levels in it.

Additionally, some players choose to sign-in as Undeclared for various personal reasons, holding onto them for pride, or to give the land credit for having a player attend without having to deal with choosing/participating in class battlegames.

Amtgard Character Classes
Core Classes: Anti-Paladin · Archer · Assassin · Barbarian · Bard · Druid · Healer · Monk · Paladin · Scout · Warrior · Wizard

Non-Standard Classes: Monster · Peasant
Alternate Sign-ins: Color · Undeclared