Valet parking and Meet and Greet parking are very similar and often used interchangeably. Valet parking is often operated by the airport itself and offers a drop off service right outside the terminal. Meet and Greet parking is more often a trusted, off-airport operator (although airports also run their own Meet and Greet services too) that offers a drop off service in a dedicated on-airport car park, that's a short walk from the terminal.