Abbreviation for Digital Subscriber Line. DSL is a high-speed method of sending computer data over standard copper telephone wires using sophisticated modulation techniques. There are several types of DSL connections, but they all require a special DSL modem between your computer and the phone line. DSL’s are sometimes referred to as “last mile” technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations. This also means you have to be within an acceptable range of a telephone switching station in order for it to work well enough to be useful. DSL has become popular the last few years as a really fast and reasonably affordable way of connecting home or office computers to the Internet.