WordPress includes the ability to have an unlimited number of users. Each of the users can be assigned one of the five (or six) roles. Let's look at these roles one at a time, starting with the most powerful.
Even though it sounds very appealing, the Super Admin (aka Network Admin) role isn't actually that fancy. Basically, WordPress has now allowed users to build a multisite setup (mentioned a couple of pages ago). This is a scenario where you have more than one site built on just a single WordPress installation. Now, the Super Admin is a role that has complete administration access to all websites that are part of a given multisite network.
Honestly speaking, if you don't have any multisite structure set up on your WordPress installation then you won't even see the Super Admin role in the WP Admin.