The Harry Potter series discusses many spells created by particular wizards like Snape and Voldemort. What does it really mean to create a spell?
Does the creator select a befitting Latin phrase and certain wand movements to channel the magic inherent in him? More importantly, how does he/she seal these for use by all future wizards?
The first may be all right, since it seems suggested in the series that, in principle (i.e., with sufficient ability, expertise in channelling magic etc.), any spell could work non-verbal and wandless. It is the second subquestion above that demands an answer.
After all, every spell discussed had to be created at some point in the past, since Latin had a beginning in history.