Cursed were (Qutila) the People of the Ditch (Ukhdud).
meaning, the companions of the Ukhdud were cursed.
The plural of Ukhdud is Akhadid, which means ditches in the ground.
This is information about a group of people who were among the disbelievers. They went after those among them who believed in Allah and they attempted to force them to give up their religion. However, the believers refused to recant, so they dug a ditch for them in the ground. Then they lit a fire in it and prepared some fuel for it in order to keep it ablaze. Then they tried to convince them (the believers) to apostate from their religion (again), but they still refused them. So they threw them into the fire.
Thus, Allah says,
قُتِلَ أَصْحَـبُ الاٍّخْدُودِ
النَّارِ ذَاتِ الْوَقُودِ