A Digital Subscriber Line Access Multiplexer. It is a box that sits in leased space in the local office of your local telephone utility. It takes a bunch of (relatively) puny DSL lines and MUXes them into a fiber pipe that gets sent up to bigger fish in the internet pond.

If a potential job description mentions DSLAMS, you probably don't want it, because you'll have to work with phone companies, which are pretty evil.