wiki?

[ScottChapman]

I see that there is an email account created for document management called wiki.

Is there any documentation on what it is for and how to use it?

[p24t]

I believe that is used for the Documents feature. You can enable Documents in your CoS, or per-user, if it is disabled.

[ScottChapman]

Then what is that wiki email address for?

[mmorse]

Read this: Using_the_Global_Documents_Account : Documents - Enabling for 4.0 Upgrade - Zimbra :: Wiki. (ignore the misleading title & you already have the global initialized)
For instance you may decide to create a domain level wiki account, assign permisisons, then users can mount it as a share.

[Bill Brock]

If you are going to seriously use Documents you'll want to vote for Bug 27820.