'Angel' means messenger. Sometimes we use that for the type of supernatural being that was often used as a messenger. I do not know if these beings deliver messages. The word for 'seraph' in Isaiah 6 is translated to refer to types of snakes/serpents in other passages in Isaiah. Isaiah may have seen some kind of winged snake creatures with six wings that cried " Holy, holy, holy, is the Lord of hosts: the whole earth is full of his glory." Is that being a messenger? I know of no case where they are called 'angels.' Cherubim may be throne guardians or transporters. In Ezekiel, they have the face of a man, the face of a lion, the face of an eagle, and the face of an ox, wings, and eyes. I know of no scripture where they are called 'angels.'
Angels be a different type of creation from these other two creatures. Then they might technically be 'angels' when delivering a message. It could be they are called 'sons of God' or 'elim' in different contexts, or there may be angelic beings who served as angels who do not fit into this (or these) category(ies). There are traditions about hierarchies of angels. I do not see how we can arrive at all of these ideas from scripture, though. A lot of this is a mystery. Since angelic type beings work behind the scenes from our perspective, we may not need all the details in this age.