What's the difference between "ortibal" and "orbit"? Which one should be used in physics? In quantum mechanics, is "atomic orbital" or "atomic orbit" used? And what about in classical mechanics? A particle's orbit or orbital?
An orbit is a closed trajectory of a classical dynamical system.
Properties of orbits or related to orbits are referred to as orbital properties.
An orbital is a single-electron wave function for an atom or molecule in the Hartree-Fock approximation. (There are also hybrid orbitals for electron pairs in a chemical bond.)
Thus a particle has an orbit (and related properties such as orbital speed) if it is treated classically (e.g., a planet). But if treated by quantum mechanics (e.g., an electron), it instead has orbitals.
In quantum mechanics, strictly speaking, it's usually "orbital" (http://www.chemguide.co.uk/atoms/properties/orbitsorbitals.html ), in classical mechanics, it's "orbit". But classical mechanics is not very good for atoms.