Dropped frames occur when there is missing data from your DV tape. What happens is there are usually tiny gaps, maybe only one or two frames, where there is missing footage on the tape. This can happen when recording often, as the camera does not always print footage to tape efficiently. In the editing program in which you are capturing, the video will give you the option to either abort dropped frames or allow them in the capture. If you are set to abort then the second that dropped frames are detected then the capture will be canceled and all footage will be lost. If you allow the dropped frames to be ignored then you will have choppy or stalling footage for your editing.