Stands for "Digital Subscriber Line Access Multiplexer." A DSLAM is a device used by Internet Service Providers (ISPs) to route incoming DSL connections to the Internet. Since a "multiplexer" combines multiple signals into one, a DSLAM combines a group of subscribers' connections into one aggregate Internet connection.
For example, a DSL access multiplier may receive signals from all the DSL modems in a certain neighborhood and patch them through to the Internet backbone. The DSLAM processes each incoming connection and may limit the bandwidth of certain DSL lines. Most DSL service providers use multiple DSLAMs to help route incoming and outgoing traffic in the most efficient way possible.