A watch combining multiple major complications in a single movement, traditionally requiring at minimum a chiming mechanism, a chronograph, and a calendar complication together.
Grande complication has no single, universally enforced definition, but the traditional benchmark requires a watch to combine at least three categories of complication: a striking mechanism such as a minute repeater, a chronograph, and a calendar complication, typically a perpetual calendar. Meeting all three in one movement demands an enormous number of additional components and a correspondingly difficult assembly process.
In practice, the term gets used more loosely today to describe any watch stacking several significant complications, even without a chiming mechanism present. Purists tend to reserve it for watches meeting the stricter historical definition, and treat looser usage as marketing shorthand.
The traditional definition requires at least three categories together: a striking mechanism (like a minute repeater), a chronograph, and a calendar complication, usually a perpetual calendar. Modern usage is often looser than this.
It has a genuine technical definition rooted in combining major complication categories, but it's increasingly used more loosely in modern marketing to describe any watch with several significant complications.
Combining multiple major complications in one movement requires an enormous number of additional components and a far more difficult assembly and adjustment process than any single complication alone.