A bridged tap is an unterminated section of wire that can interupt or create disturbances on a transmission wire. It sometimes involves a technique for a telephone install that taps you into a line that runs past your house, rather than terminating directly to your house. The line doesn't neccesarily go to any other customer premises, it just ends.

The phone company can simply add a tap up or down to service wire whenever customers move or a change in service is needed. Unfortunately, you have unterminated phone line running up the road ready to pick up any interference, like a huge TV antenna. Because it's not terminated properly, the signals are reflected and bounce up and down the line and can reinforce or cancel the signals your equipment is trying to send to your ISP.