What is superstition?

Superstition is the belief that certain events, objects, or patterns of behavior will bring about a particular result, regardless of an objective causal relationship. Superstitious belief may be cultural, religious, or based on personal, subjective experiences. Perhaps you know of some superstitions in your culture-- where I grew up, some people believe that black cats are a sign of bad luck!
An example of a cultural superstition would be something like belief in black cats causing bad luck, or that if you spill salt and fail to throw it over your shoulder, something bad will happen. Not all superstitions are so much about avoiding or remedying negative events; many are about inviting positive events into your life. Some people believe that if they carry a rabbit's foot key chain, they will have good luck.
An example of a religious superstition would be something like a "Bible-dip." Some Christian people believe that when they need advice on a particular matter, they can open a Bible to a random page and take advice from the first passage they read.
A rather famous example of personal superstition is Dennis Grossini. One day before a game, he went to a nearby restaurant, had two glasses of iced tea, and ate a tuna-fish sandwich. That day, he played especially well in his baseball game. He came to understand his luck in the game as having been caused by his actions of the morning, and for the next three months he did the same thing before every game! 
Superstitions aren't necessarily based on any verifiable cause-effect relationships, but rely on perceived experience of positive and negative consequences. 
https://www.britannica.com/topic/superstition