DRADIS (Direction, RAnge, and DIStance) is a detection, identification and tracking system, somewhat similar to radar, used aboard colonial warships. Much like real world radar, there are also stationary DRADIS stations. The Cylons were able to jury-rig the DRADIS assembly from a Heavy Raider into a stationary DRADIS tracking array. ("Fragged")
This is an unfortunate acronym, since "range" and "distance" are redundant with each other.