What do we call a formal event held in honor of a special occasion?

A formal event held in honor of a special occasion is referred to as a ceremony. Ceremonies typically have a structured format and may include rituals or specific protocols, making them distinct from more casual gatherings or celebrations. A ceremony often marks significant events like graduations, weddings, or award presentations, where the intent is to honor achievements, commemorate events, or acknowledge important moments in a formal setting.

In contrast, while a festival may also celebrate an occasion, it often involves a series of events or activities for entertainment or enjoyment and lacks the solemnity or formality of a ceremony. A celebration is broader and could encompass various forms of acknowledgment, but it does not inherently connote a formal structure. Similarly, a gathering may refer to any assembly of people, which may or may not include a formal element or special occasion. Thus, "ceremony" best encapsulates the nature of a formal event honoring a significant occasion.