An invocation is an appeal to a higher power for help, such as a prayer for serenity or a plea to the rain gods during a drought.
An invocation often refers to an appeal to something not of this world, such as a god or a spirit, but it can involve an appeal to any higher power, even one that is flesh and blood. During a close basketball game, for example, you may mutter an invocation to the former NBA star Michael Jordan asking that your team’s star player somehow gain the power to hit his jump shots. The word invocation can also be used in the sense of invoking a notable authority to support a position. If you say, “But my mom said I should never wear cheap clothing,” for example, that is an invocation of your mom in support of your desire to buy designer jeans.