What is the difference between system admin, server admin, windows admin?

System admin will trouble shoot your systems problem if required.

Server admin every time he should keep his eyes on event log and its security, watching that all users using properly.

windows admin only he can proived that your operating application are working properly. 

System admin will manage all type of server and client whereas server admin is manage only server machine and window admin will maintain only windows machine

System admin will manage all types of OS (Client end and server end ) , Server Admin will manage all types of server and Windows admin will manage only Window based operating systems

A system administrator, systems administrator, or sysadmin, is a person employed to maintain and operate a computer system and/or network. System administrators may be members of an information technology department. a server administrator, or admin has the overall control over a game/ application/ computer/ network server within that.The admin for a server typically represents the owners and financiers of the server. Alternatively, an owner can grant administrator rights to a regular user (or clan member) on the server.