Basically a car-bomb stuffed into an disused oil barrel (NH₄NO₃ and Diesel fuel w/nails, bolts, and other improvised shrapnel) then dropped from high altitude -out of the range of small arms fire- the government has already killed 20,000 with the crude-yet-effective device...
They started tossing them out of Russian-made Hind helicopter gunships over a year ago, and to especially devastating effect in the government's pounding of Allepo a couple months back.
Though just a barrel full of stuff that blows up and spews nails/etc all around, part of it's effectiveness in the government terror campaign has been how indiscriminate the barrels are in choosing their victims- instilling sheer terror.
Syrian gunship dangles barrel-bombs prior to release
Yet somehow the Syrians felt the need for increased accuracy, and many see the hand of Russia, who must be offering know-how to the Syrian Army in making the barrel-bombs more sophisticated: i.e. tail fins for guidance and a contact fuse that detonates on impact, rather than the guesswork of the live,
lit fuses utilized of last year.
But it's not like the other side's any better...