Based on these videos, which like so much rebel-made media out of the Syrian conflict are unconfirmed and should be taken with a grain of salt, it appears that a rocket or missile slammed into the side of a helicopter. The aircraft bears some resemblance to an Mi-8, which like much of the Syrian military arsenal is Russian-made.
The EA Worldview blog writes of the reports, "The speed at which these videos were posted, and the speed at which the eyewitness reports [surfaces] that did NOT include the videos, adds credibility that at least one helicopter was shot down." The blog adds, "We're cautiously optimistic that all three videos will be confirmed as showing the same helicopter." A Syrian activist on claimed on Twitter that the video shows "captured anti-craft missiles."
This first video appears to show the impact, followed by cheering in Arabic:
The second seems to show the scene immediately after, with flames visible on the side of the smoking helicopter:
In this final video, a helicopter – apparently the same helicopter and the same scenery as the other videos – losing altitude before it crashes into the ground:
Syrian government forces have dominated the skies since the first days of the uprising in 2011. The military's airpower monopoly has allowed it to wreak havoc on less well-equipped rebels and on civilian-filled urban areas. One successful rebel shootdown of a government helicopter is not, on its own, likely to dramatically change this dynamic. But it would be an important landmark in the long and difficult war.