Karma is a word that is about the cycle of cause and effect.
According to the theory of Karma, what happens to a person, happens because they caused it with their actions. It is an important part of many religions such as Hinduism and Buddhism.
In terms of spiritual development, Karma is about all that a person has done, is doing and will do. Karma is not about punishment or reward. Karma makes a person responsible for their own life, and how they treat other people.
Karma is a useful teacher, forcing people to face the consequences of their actions and thus improve and refine their behavior, or suffer if they do not.
Even harsh karma, when faced in wisdom, can be the greatest spark for spiritual growth.