"Magic has three parts... power to change reality, focus to direct that change, and an effect, that change in the real world." Jenkins, "And the Horns of a Dilemma"
Throughout the TV series (although not in the TV movies), the concept is constantly revisited that magic is power, focus and effect.
Power - The energy or force which makes an unnatural change in the environment or individual possible.
Focus - The item or spell which serves as a lens and lathe for the desired outcome, usually designed at the time of its creation for a specific purpose.
Effect - The consequence in the world of the magic being unleashed. Although it is not directly stated, this is often implied to include the price to the wielder of deploying the magic.
To a considerable degree, the three newer Librarians reflect these aspects, with Jacob often providing the power, Cassie the focus and Ezekiel the unexpected effect when most needed.