A group of owls is called a parliament. There are other collective nouns in use for groups of owls, including flock, but parliament is the most frequently cited word.
Other words that have been claimed for groups of owls include stare, congress, glaring, hooting, bazaar and sagaciousness, according to the Baltimore Bird Club. Many of these make reference to the owl's large staring eyes or to their solemn appearance. Many species of owl are solitary, so seeing a flock or parliament of owls is a rare event indeed. On a strictly scientific level, the two groups of birds which contain owl species are the family Tytonidae and the family Strigidae.