NTN may refer to any of the following:
1. The network terminal number (NTN) is a set of digits that make up the full address of the end point to a data terminal. It is either a ten or eleven digit number found in the CCITT (International Telegraph and Telephone Consultative Committee) X.25 14-digit address.
The NTN is ten digits in length when it is not part of a national integrated numbering format. When it is part of a national integrated numbering format, it is eleven digits in length. In both cases, it follows the Data Network Identification Code (DNIC) in the CCITT X.25 14-digit address.
2. NTN is also chat slang for "nothing."