What is a superstition?

In presenting cultural diversity workshops to staff, we as a group not only discuss our backgrounds and learn from each other but we also share our common personal values passed down from our generations like diversity, equality, trust, truth and many others.  Among our discussions, superstitions are brought up.  Some are very interesting.

What is a superstition? 

The dictionary states: It is an irrational belief that an object, action,
or circumstance not logically related to a course of events influences its
outcome like a black cat walking across in front of you or going under a
ladder.

Do have any superstitions?