Yes, beholders are aberrations in D&D 5e. People probably think of them when they think of an oddity. About all, there is to say about aberrations in D&D 5e. They're meant to be completely strange and almost scary creatures, no matter where they are. They are based on cosmic horror monsters and other things like Cthulhu. Aberrations come from places beyond the outer planes, but they usually live underground or in the water.