Super admin and System admin are more commonly used as they come from the best practice (which is nowadays an upgrade we can do to obtain such Permission roles and Permission groups), but Security admin is not a common one (maybe a reference to Grant Role Based Permission access, as that goes outside of RBP in order to grant someone access to it and to the option to grant someone access to it).
A super admin would normally be someone with all permissions (perhaps a few checkboxes excluded as those are meant to reduce access). This means they have a permission role and group for System Admin that provides them with the maximum amount of access (i.e. Admin that can do anything in Employee Central, Performance and Goals etc.). So permissions range from higher level features such as permissions and imports to making transactions for employees.
A system admin is more commonly someone that performs administrative activities per employee, i.e. Giving an employee a promotion, creating a new hire, terminating an employee, creating/updating a position. This person would however not have access to bigger features such as mass changes, imports, permission roles and groups or configuration related features such as manage business configuration, configure object definitions, configure people profile etc.