I once had a student (about 18) ask what's the difference between myth, superstition and religion. As an on the spot question, I had a hard time giving a solid, honest and intelligent answer without the benefit of time to think about it. After going home to ponder it, I'm still not sure of the answer
My personal definition - If it's a cool story that no one takes literally anymore, it's a myth - Virtually no one
believes in the Greek or Norse myths anymore - they may have been religions once, but they've fallen to the level of myths. One should also note the presence of the phenomenon called urban myth, which is an improbable, but cool story often believed by many and that requires the combined efforts of Jamie and Adam to disprove it.
If it's your belief system, it's superstition. If it's mine, it's religion.
More seriously, a superstition could be a belief that has little/no factual basis and (usually) not directly tied into religious beliefs. It's often (but not always - I'm sure someone has some counter-examples) possible to apply a little science to show that a superstition isn't true. For example, we blindfold 1000 people and randomly have them walk down one of two paths. One is just a path. The other has them walk under 5 ladders while 13 black cats cross the path. We can then follow these people and monitor them for health and employment status changes and (hopefully) show that there is no statistically significant difference.
A religion is typically based on faith and isn't very easily placed under scientific scrutiny (ok, some specific elements may be testable, but general faith in divinity isn't so simple to deal with in the lab). If I believe that God set off the big bang, it won't be easy to design an experiment to prove me wrong (or right). If I believe that God delivers divine messages via the Pope, some Buddhist leader, or directly from Raoul, it won't be easy to prove this to be incorrect, unless one of these messengers decides to make statements that are subject to independent verification. If I believe that the afterlife is an eternal foot massage administered by the prettiest possible Chinese girls, you can hope I'm right and even join me in this belief, but you probably can't prove or disprove it.