New to me at any rate.
A double ended metal halide lamp that contains TWO discharge bulbs, connected in series.
Presumably intended for use with a series magnetic ballast on 380/400/415 volt circuits, or an electronic ballast.
https://www.ebay.co.uk/itm/182544154056?_trksid=p2485497.m4902.l9144ebay link included, not by way of recommendation but show the type of product to which I refer.