CBDR is an acronym for Constant Bearing, Decreasing Range, and refers to an object on an intercept (or collision) course with a ship. Cylon Raiders closing on Galactica can be CBDR ("Final Cut"), and when Pegasus first appeared on DRADIS it was described as CBDR to Galactica ("Pegasus").
Re-imagined Series definition: Constant Bearing, Decreasing Range. Indicates object on a collision course (TRS: "Final Cut", "Pegasus")