A commode could also refer to a low-lying set of drawers, or a portable washstand with a cupboard hidden beneath the counter top. The definition of commode which most closely matches this discussion is a boxy structure which conceals and supports a seat over a removable chamberpot or bedpan. The key idea of a true commode is portability. A commode is not connected to water or sewer lines, but serves more as a privacy chamber for users on the move, so to speak. The commode would find the user, not the other way around.
A toilet, on the other hand, is considered a permanent plumbing fixture. The porcelain bowl and tank attached to the floor of a bathroom or loo or water closet can always be called a toilet. Although the term toilette can also refer to a woman's vanity or dressing table, the derivative toilet refers solely to a water-filled fixture used for waste elimination. In the strictest sense, a bedpan or portable toilet seat with an attached dry receptacle would be a commode, while the water-flushed bowl and tank in the bathroom would be a toilet.
It is not unusual for terms such as commode or toilet to be used interchangeably as different cultures begin to blend. Asking for the nearest bathroom in Great Britain, for example, may lead to some bemused looks, because they refer to that destination as the loo or water closet or WC. In certain Asian countries, there is no such fixture as a commode or toilet. Users must squat over a designated opening in the floor to conduct business. A separate cleansing fixture known as a bidet may deliver a surprising jolt of clean water to unsuspecting users in some European locations.
In short, the only real difference between a commode and toilet is portability, although few people alive today can remember a time when a portable commode would have been used in place of a flush toilet in a modern home.