ISDN stands for Integrated Services Digital Network. It is a type of communication technology that was commonly used in the 90s and early 2000s to transmit voice, data and video over digital phone lines.
ISDN works by converting analogue signals into digital signals, which allows for faster and more reliable communication over phone lines. It offers features such as faster call setup times, higher quality voice and video calls and the ability to transmit data over the same line as voice calls.