Windows Server is a brand name for a group of server operating systems released by Microsoft. wikipedia.org

A system administrator, or sysadmin, is a person who is responsible for the upkeep, configuration, and reliable operation of computer systems; especially multi-user computers, such as servers. wikipedia.org

Active Directory (AD) is a directory service created by Microsoft for Windows domain networks. wikipedia.org

A help desk is an information and assistance resource that troubleshoots problems with computers or similar products. Corporations often provide help desk support to their customers via a toll-free number, website and e-mail.

A network administrator, network analyst or network engineer is a person responsible for the maintenance of computer hardware and software that comprises a computer network. This normally includes deploying, configuring, maintaining and monitoring active network equipment. wikipedia.org

Customer service is the provision of service to customers before, during and after a purchase. wikipedia.org

Technical support or tech support refers to a range of services by which enterprises provide assistance to users of technology products such as mobile phones, televisions, computers, software products or other electronic or mechanical goods.

A virtual private network (VPN) is a network that uses primarily public telecommunication infrastructure, such as the Internet, to provide remote offices or traveling users access to a central organizational network. wikipedia.org