A formatted, block-oriented, high-reliability, random access tape system used on the Laboratory Instrument Computer. The tape was 3/4" wide.
The funny DECtape is actually a variant of the original LINCtape. According to Wesley Clark, DEC tried to "improve" the LINCtape system, which mechanically, was wonderfully simple and elegant. The DEC version had pressure fingers and tape guides to force alignment as well as huge DC servo motors and complex control circuitry. These literally shredded the tape to bits if not carefully adjusted, and required frequent cleaning to remove all the shedded tape oxide. That was amazing, because the tape had a micro-thin plastic layer OVER the oxide to protect it. What happened was that all the forced alignment stuff caused shredding at the edge.
An independent company, Computer Operations[?], built LINCtape drives for use in nuclear submarines. This was based on the tape system's high reliability. Correspondent Brian Converse has a picture of himself holding a LINCtape punched full of 1/4" holes. It still worked!