DSL is a type of broadband connection.  It stands for Digital Subscriber Line, and is offered by traditional phone companies (wired, not wireless).  The signal travels thru phone lines and into your home or business.  A modem is connected to it so it can translate the signal into ditigal data and then is usually output via Ethernet.  Its main competitor (at least in homes)is Cable broadband.  The difference between the two is that cable generally provides faster bandwith (download/upload speed), but is less secure than DSL, which provides each user with a unique IP (Internet Protocol)address.  Most cable internet home subscribers are connected to a router with up to 255 other subscribers, making attacks and intrusions much more likely.
DSL vs. broadband?