What is a DLT? Why is a DLT better than a recordable DVD?

DLT stands for "Digital Linear Tape". DLT is still very much the preferred format for supplying DVD masters for replication. It has bullet-proof error-correction, which guarantees that the pressed disc will work exactly as you intend. By contrast, recordable DVD discs suffer from quality issues, scratches, fingerprints etc - and any one of these can cause a failed glass master at the replication stage. This can cause delay, and in the worst case cost you money.