Final answer:
The method used by social movements to form shared meanings motivating collective action is called the frame alignment process, which is part of frame analysis.
Step-by-step explanation:
The method by which social movements create shared meanings and definitions that inspire and justify collective action is known as the frame alignment process. This method is a part of frame analysis, a sociological concept that describes how individuals identify and understand social events and decide upon the norms to follow. The frame alignment process involves using tactics like bridging, amplification, extension, and transformation to recruit and align participants' attitudes and beliefs with the goals of the movement, which facilitates the process of building a collective identity and motivates them to partake in the movement.