DSL stand for Digital Subscriber Line. DSL provides high speed on already exiting telephone lines and same time you can use internet and as well as your line for phone. In DSL, both ends of connections require the network cards and DSL modems for data communication.
Your DSL connection to the Internet will always on, there is not need to dial your ISP each time to use internet. DSL is much easier to install and provides much faster data transfer rate. Its data transmission speed start from 128 Kbps up to 10 Mbps. DSL connections are more useful in applications like videoconferencing, to run online movies and upload and download heavy files. There are different flavors of DSL like ADSL, R-ADSL, HDSL, SDSL, and VDSL.
The ADSL and HDSL are very common in use, the former being more popular for home usage.