Seraphim is plural, SERAPH is singular. SERAPH means burning one.
"A seraph (/ˈsɛr.əf/; pl. seraphs or seraphim /ˈsɛr.ə.fɪm/; Hebrew: שְׂרָפִים śərāfîm, singular שָׂרָף śārāf; Latin: seraphi[m], singular seraph[us]; Greek: σεραφείμ) is a type of celestial or heavenly being in Judaism and Christianity.
Psalm 104:4 KJV
King James Version
Who maketh his angels spirits; his ministers a flaming fire:
Hebrews 1:7 ; King James Bible "And of the angels he saith, Who maketh his angels spirits, and his ministers a flame of fire."
Literally "burning ones", the word seraph is normally a synonym for serpents when used in the Hebrew Bible. A seminal passage in the Book of Isaiah (Isaiah 6:1-8) used the same term to describe fiery six-winged beings that fly around the Throne of God crying "holy, holy, holy". This throne scene, with its triple invocation of holiness (a formula that came to be known as the Trisagion), profoundly influenced subsequent theology, literature and art. Its influence is frequently seen in works depicting angels, heaven and apotheosis. Seraphs are mentioned as celestial beings in an influential Hellenistic work, the Book of Enoch, and the Book of Revelation. Tradition places seraphs in the fifth rank of ten in the Jewish angelic hierarchy and the highest rank in the Christian angelic hierarchy."
from Wikipedia Christianity and Judaism
Verse 4. Who maketh his angels spirits; or wields, for the word means either. Angels are pure spirits, though they are permitted to assume a visible form when God desires us to see them. God is a spirit, and he is waited upon by spirits in his royal courts. Angels are like winds for mystery, force, and invisibility, and no doubt the winds themselves are often the angels or messengers of God. God who makes his angels to be as winds, can also make winds to be his angels, and they are constantly so in the economy of nature.
His ministers a flaming fire. Here, too, we may choose which we will of two meanings: God's ministers or servants he makes to be as swift, potent, and terrible as fire, and on the other hand he makes fire, that devouring element, to be his minister flaming forth upon his errands. That the passage refers to angels is clear from Hebrews 1:7 ; King James Bible "And of the angels he saith, Who maketh his angels spirits, and his ministers a flame of fire."
-Commentary of Psalm 104:4.