The "Four Schools" refers to Shandong's (called after its former polity of Lu), Jiangsu's (called Yang after its most famous branch), Cantonese (called after its former polity of Yue), and Szechuan's (abbreviated to Chuan) cuisines.
Eventually, four of these branches were recognized as distinct Chinese schools themselves: Hunan's cuisine (called Xiang for its local river), Fujian's (called Min for its native people), Anhui's (abbreviated as Hui), and Zhejiang's (abbreviated as Zhe).