Seraphim are heavenly beings mentioned only twice in the Bible (Isaiah 6:2, 6). "Seraph" is the singular form, referring to one being, while "seraphim" is the plural form, referring to more than one.
Isaiah does not say exactly how many seraphim he saw in his vision. He describes them as though they were familiar heavenly beings, even though they are not mentioned elsewhere in the Bible.
Isaiah described each seraph as having six wings:
two shielded the face,
two covered the feet,
and the remaining pair enabled the seraph to fly.
Based on the available evidence, the seraphim were heavenly beings who held a place of honor and continually praised and worshiped God. They were probably a group of heavenly beings similar to the cherubim, who also served near God's throne.
See also Angel; Cherub, Cherubim.