Realms
Realms are used as a way to group users. The most common way to group them is by using the DNS name of an organization. This name is then separated from the user's name with a special character referred to as a delimiter. Again the most common delimiter is the '@' character although other characters can be used. The result is a username similar to an e-mail address (alice@my-org.com). Although the username may look like an e-mail address there is absolutely no requirement for it to be a valid e-mail address.
Other common conventions used for realm grouping includes user%realm, realm\user, or realm/user. These are, however, less popular.
