When combined, 盛大 (shèngdà) literally means “flourishing and big” or “abundantly large.” This fusion perfectly captures the modern meaning: an event that is impressive not just in its physical size (大) but also in its richness, splendor, and prosperous atmosphere (盛).
The concept of 盛大 (shèngdà) is deeply connected to the cultural importance of 场面 (chǎngmiàn), or “spectacle,” and 热闹 (rènao), a lively and bustling atmosphere, in Chinese society. For significant occasions—be it a company's anniversary, a new store opening, or a national holiday—making the event 盛大 is a way to display prosperity, success, respect, and importance. A grand event generates “face” (面子, miànzi) for the organizers and shows honor to the guests. A useful Western comparison is the difference between a “big party” and a “gala.” A “big party” simply implies a large number of attendees. A “gala,” however, is implicitly 盛大. It suggests formality, elaborate decorations, a significant purpose, and a sense of splendor. While Americans might value a “laid-back” or “casual” large gathering, Chinese culture often prefers key events to be 盛大 to properly reflect their significance.
盛大 (shèngdà) is a formal adjective. You will encounter it most often in news reports, formal announcements, and descriptions of significant public or private events.
Its connotation is almost always positive and celebratory. You would not use it for a large traffic jam or a big problem.