one definition, that Jamie always likes, is that "magic is getting something for nothing"
Like, if you have a cake recipe that needs an egg in it, but you say some magic words in place of an egg and then the cake appears even though you have 0 eggs, that'd be magic
Because at no point did the actual work that needs to have happened to make the cake have that ingredient, there's no logic between saying words and an egg being in a cake