Final answer:
The relationship stage with a formal commitment recognized by custom or law is engagement, leading to marriage, a legally recognized and socially structured union.
Step-by-step explanation:
The relationship stage where a formal statement of commitment is made between two people, often recognized by customs or law, is called engagement. This stage is characterized by the exchange of rings, specific rituals, and a period of preparation for marriage. It is an acknowledgment that the relationship is transitioning towards marriage, which is a legally recognized social contract that may be based on a sexual relationship and implies the permanence of the union. In sociological terms, marriage involves the formation of a socially recognized union that often provides a structure for raising offspring, creating alliances, and obtaining social, political, and economic advantages.
Throughout this process, there are cultural variances and practices regarding romantic involvement, orientation towards mutual love or arranged negotiations, and the roles and symbols associated with the relationship. Ultimately, the engaged couple will move towards the next stage, marriage, which solidifies their union as per social and legal standards, often involving rituals that signify their new social status and identity.