In this document, we define a system administrator as the person who is responsible for the system/server where the TYPO3 instance is installed. System administrators usually have full access on a server level (operating system) and install, configure and maintain the base system and hosting environment, including the database server, web server, PHP, TYPO3, as well as components such as ImageMagick, etc.
System administrators are also responsible for the security of the infrastructure in general, e.g. the network, the appropriate access to the system (e.g. SSH, FTP, etc.) as well as correct permissions on a file system level.
The role of a system administrator often overlaps with a TYPO3 integrator and it is likely that one person is in both roles.