Which word describes the orderly movement at the beginning of a service?

The term that best describes the orderly movement at the beginning of a service is "Procession." A procession typically refers to a formal, organized flow of individuals, often leading into a venue, such as during a religious service or ceremonial event. This movement is characterized by its structured nature and purpose, usually signifying the start of a significant occasion where participants may include clergy, choir members, or other designated individuals following a designated path.

In contrast, other terms like "Recession" often refer to a formal exit or departure, which does not align with the concept being assessed. "Assembly" denotes a gathering of people, but without the specific connotation of a formalized entry. Similarly, "Gathering" refers to simply coming together in one place and lacks the structured, ritualistic aspect associated with the term "Procession." Therefore, the choice of "Procession" directly aligns with the context of orderly movement at the beginning of a service, making it the appropriate term to describe that scenario.