I can’t answer what Bombadil is in the lore of LOTR, he seems to be unique in terms of entities we are shown. But I can tell you what he is at a meta level. You see, LOTR was first told as stories to Tolkiens kids, which you probably already knew, which you may not have known, is that Bombadil was a recurring character in previous stories he had told his children. So at a meta level, Bombadil is just a fun callback to a previous character for his kids to have enjoyed.
I can’t answer what Bombadil is in the lore of LOTR, he seems to be unique in terms of entities we are shown. But I can tell you what he is at a meta level. You see, LOTR was first told as stories to Tolkiens kids, which you probably already knew, which you may not have known, is that Bombadil was a recurring character in previous stories he had told his children. So at a meta level, Bombadil is just a fun callback to a previous character for his kids to have enjoyed.