麦 is McDonald's signature syllable in Mainland Chinese —
麦当劳 (Màidāngláo) is the brand itself, and many products use
麦 as a prefix:
麦乐鸡 (McNuggets),
麦乐送 (McDelivery),
麦辣鸡腿堡 (Spicy McChicken).
麦乐 reads roughly as 'wheat-fun', a friendly-sounding pair.