Potential

Potential is a term Kyubey uses in Madoka Magica. While the potential of any given Magical Girl is never explicitly said, Kyubey gives clues and sequences to help estimate the potential of any given girl to become a Magical Girl

Explanation

In order to become a Magical Girl, a girl in puberty must have a high enough potential.

Kyubey explains that the placement of a girl in her respective standing in the social sphere in the amount of potential a girl has. For example, it states, a girl who is a princess will have more potential than a peasant girl.

Additionally, the amount of potential decides how strong or accurate the wish is. For example, (spoilers for Tart Magica and The Different Story) Lapin (link) made a wish for Isabeau (link) to become human again after becoming a Witch. This, however, did not work as expected. Isabeau's body was a husk, and the Witch took over her body. in The Different Story, however, Madoka (link) makes a wish for Sayaka (link) to "de-witchify" (link). Unlike Isabeau, however, the process worked. It can be assumed that even though both Lapin and Madoka made similar wishes, the potential difference between their potentials affected the strength or "accuracy" of the wish.