xDSL in IT Glossary

Refers collectively to all types of digital subscriber lines,
the two main categories being ADSL and SDSL. Two other types
of xDSL technologies are High-data-rate DSL (HDSL) and Very
high DSL (VDSL).
DSL technologies use sophisticated modulation schemes to pack
data onto copper wires. They 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.

xDSL is similar to ISDN inasmuch as both operate over existing
copper telephone lines (POTS) and both require the short runs
to a central telephone office (usually less than 20,000 feet).
However, xDSL offers much higher speeds - up to 32 Mbps for
upstream traffic, and from 32 Kbps to over 1 Mbps for downstream
traffic.