There is no concrete definition of the term "meal" in the Income Tax Act, the wage tax guidelines or the BMF letter dated 18.01.2019. The following definition has emerged over the years as a result of various rulings, appeals, BMF letters and recognized practices:
Food is deemed to be reimbursable if it is suitable for immediate consumption or is intended for consumption during meal breaks - this also includes beverages customary for meals if they are consumed in connection with a meal.
Meals are basically all meals and foodstuffs that are normally used for nutrition and are suitable for consumption during working hours or immediately afterwards.
Sources:
BFH rulings from 21.3.1975 - BStBl II p. 486 and from 7.11.1975 - BStBl 1976 II p. 50
R 8.1 para. 7 no. 4 a) double letter aa) LStR