Final answer:
James Marcia defines commitment as a personal investment in identity, which is a part of his identity status model in the context of individual identity formation.
Step-by-step explanation:
James Marcia's theory of identity development involves understanding different ways in which individuals approach their own identity formation. According to Marcia, commitment is defined as a personal investment in identity. This concept involves making choices about one's beliefs and values, and demonstrating a commitment to certain goals, professions, or ideologies. It is an integral part of Marcia's identity status model, which also includes other statuses such as identity diffusion, foreclosure, and moratorium, each representing different approaches to the process of identity development.