Luncheon refers to a meal served around midday and is more commonly used for special meals rather than daily lunch. The club scheduled a luncheon for the visiting author.
Pro Tip 2/3
Not Always Formal
While 'luncheon' sounds formal, it can be used for casual get-togethers as long as it's a planned meal. We're having a friendly luncheon at my place next week.
Pro Tip 3/3
Cultural Usage
In some cultures, 'luncheon' may sound outdated; familiarity with modern usage is essential. My grandmother invited us to a Sunday luncheon.