Bucranium is a word that sounds tricky, but it really just means the Skull of an Ox. You know what an ox is, right? It's a big animal that farmers used to use to help them plow fields and carry heavy things.
The skull of an ox is a special thing because it was used in ancient times as a decoration for homes or buildings. People would hang it up on their walls or the front of their house to show that they were strong and powerful.
Sometimes people would even decorate the skull with fancy designs or jewels to make it even more special. But don't worry, nowadays we don't really use bucraniums for decoration anymore, since it's not very nice to the animal.