The rockets, named after the distinctive noise they make when they are launched, are improvised weapons made by attaching rocket motors to much larger bombs - a process that increases their destructive power while greatly reducing accuracy.
This greatly increases their destructive effect, while accuracy is lost and range is limited.
Activists has accused the Syrian government of using surface-to-surface missiles in Douma as clashes continued between opposition fighters and government forces.
In video posted online of Tuesday's attack, residents were seen scrambling to rescue a brother and sister trapped after a building was destroyed.
There were shouts of joy as the girl was pulled alive from the rubble while her brother could still be heard calling for help.
More than 60 people, including many children, were injured in the bombardment, activists said.