That is a domain name transfer tag.
This is if you were changing a domain from one registra to another and required by the internet service provider.
You would only need this if you are moving the domain for the site to a new domain hosting company. Are you?
BC does not host the domain, you can only point that domain to Business Catalyst, it wont host the domain for you too.
If your someone and you have a domain with a company and you want to transfer it to someone else you actualy just get a UDAI from "Mr Site" Themselves and move your domain to somoene else and then you can close the account with "Mr Site".
I think I understand. However, I thought I was using Business Catalyst for hosting, so am a bit confused about that. I've created a new site for my client using Muse and assumed that by publishing it using BC that I'd be hosting it for my client through BC. I guess that is wrong. Do you have any suggestions for how I go about hosting the site? My client purchased the domain name via Mr Site (I think?) and I'm not sure they are going to allow a site created outside of their template system to be hosted by them. I'm a bit green when it comes to the hosting side of things, this is the first Muse site that I've created and am on a very steep learning curve. Any help you can give me would be wonderful.