NAT

Network Address Translation
 - Allows the internal network structure of an organisation to use its own private range of IP addresses. Any traffic destined for the outside world will be translated into a real IP address for communication on the internet.

Network

Any time you connect two or more computers together so that they can share resources, you have a computer network.

NGN

Non Geographical Number
 - The United Kingdom dialling code (08XX, 09XX) is defined by OFCOM as Special Services: Higher Rate. When originally introduced, it was to be charged at no more than BT's standard national rate. A non-geographic number does not relate to any particular location in the United Kingdom like a standard geographic (01 or 02) telephone number does.

NIC

Network Information Centre - 
Generally, any office that handles information for a network. The most famous of these on the Internet was InterNIC, which was where most new domain names were registered until that process was decentralized to a number of private companies. Also means "Network Interface Card" which is the card in a computer into which you plug a network cable.

Night Service

Most telephone systems have at least two operating modes, Day Service and Night Service. These are typically used to route incoming calls to a different destination and to apply call barring to prevent unauthorised use of the phones by security or cleaning staff.

NTS

Number Translation Services
 - The service of routing a telephone call with a non-geographic number beginning with 07, 08, or 09 to a hidden geographic or mobile number.