One may not eat two cooked dishes during the last meal before the fast of Tish’a B’Av(Ta’anit 26b), because that is when our mourning over the churban intensifies, and it is inappropriate, [at such a time], to dignify oneself by indulging in two cooked items. One cooked dish, however, [is permitted, because it] does not involve any special pleasure. It is also forbidden to eat meat or drink wine [at this meal] (ibid.), because these are distinguished foods that make one happy. Indeed, the custom nowadays is to refrain from eating meat and drinking wine from the beginning of Av (see above 8.13); nonetheless, the prohibition to eat these items up until the seudah ha’mafseket is based on a custom from the time of the Rishonim, while the prohibition to eat them during the last meal is Rabbinically ordained. Therefore, a sick person or a postpartum woman, whom meat can strengthen, may eat meat during the nine days, but not at the seudah ha’mafseket.
What is the seudah ha’mafseket? It is the last meal before the fast, eaten after midday. Thus, if one eats his last meal before midday, he may eat two cooked dishes. The prevalent custom is to eat a regular meal, with several dishes, in the afternoon, and then to eat the seudah ha’mafseket, with only one cooked dish, shortly before the fast. One should not be crafty and eat a [full] meal, with several dishes, close to the fast, recite Birkat HaMazone (Grace After Meals), wait a few minutes, and then eat another meal, so that the latter will be considered the seudah ha’mafseket.
Ex post facto (b’di’avad), however, if the hour is late and one did not manage to eat a full meal in the afternoon, and he is concerned that it will be difficult to fast without eating several cooked dishes beforehand, he may eat a full meal, go to synagogue and pray Minchah, and then return home to eat the seudah ha’mafseket. He should only be careful not to eat so much during the first meal that he has no appetite to eat the seudah ha’mafseket(Sh.A. and Rama 552:9, M.B. 22).
. Even though a sick person is exempt from fasting on Tish’a B’Av, he should eat only simple foods. Therefore, he should not eat meat or two cooked dishes at the seudah ha’mafseket. See below 10.3, as well as [Hilchot Chag BeChag by] Rabbi [Moshe M.] Karp, 6:4. Only one who receives an explicit medical directive to eat meat or drink wine may do so.
It should be noted that according to the Gemara, Ta’anit 30a, one is allowed to eat meat preserved in salt and drink grape juice at the seudah ha’mafseket, because they do not bring joy. However, it is obvious that since the custom is to forbid [all types of meat and wine] starting from the first of Av, one may not eat these items at the seudah ha’mafseket.