Beelzebub is a name for a devil, often Satan himself, or a chief demon. It is a Bible name, not a word you use at the shops. In the Old Testament it names the god of a city called Ekron; the Hebrew means something like “lord of the flies.” Later Christian writing took the name as a devil. Though actually, some Bible passages treat Beelzebub as a prince of demons, not always exactly the same as Satan — teachers and churches do not all tell it the same way. You meet the name in church, in old poems, in horror stories, or as a heavy joke. It feels literary and religious, not everyday.

別西卜（聖經裡的魔王／魔鬼；和合本。天主教思高本多作「貝耳則步」）