Your "Primary" is your main character and the character you will play most of the time in raids, Primaries receive the highest loot priority in most situations.
Every member in the guild is entitled to select one of their characters as their "Secondary" character, your Secondary (or "Second"/"2nd") is a character that will receive higher priority in the loot system than other Box's, but lower priority than Primary characters in most situations. Under the current DKP system loot priority is as follows:
Expectations and Use of Secondary characters
We have a few expectations for Secondaries since they do receive a loot privilege. We expect they generally be "decently" geared. In Kunrak and beyond 2nds will be expected to have no empty gear slots, and to have generally decent group quality loot in most gear slots. They should also generally keep up with AAs to some degree, they do not need to be max AA but they should not be 0 AA characters. You are not required to have a 2nd.
If you have a 2nd, you are required to bring it to every raid you bring your main to.
2nd's pay generally 1/3rd of the "Primary" price for an item rounded down. Your 2nd spends from your Primary's DKP pool.
A Box is basically any boxed character you have that isn't a Primary or Secondary. They can participate in raids 100% at raid leader discretion, they generally can't take raid spots over Primary or Secondary. We have much lower expectations for box's than Primary/Secondary. These are essentially the "trash eating" alts, who are utilized to take rotting gear. While we have no formal expectations for box's, you still need to be a generally useful raid member. If your box is causing problems it will be asked to sit out. If you just want a character available to "take a rot", leave the character outside the raid. We expect you are still able to "effectively play" an Alt, but we understand they will often be undergeared and boxed characters so will not play to the level of a Primary character or a 2nd.
Box's pay generally 1/6th of the "Primary" price for an item rounded down. Your Box spends from your Primary's DKP pool.
A character that is on the same account as your main, secondary or box's