Making a meal of commemoration-Seudas Hodaya:
It is customary to celebrate a miracle through making a festive meal for one’s friends and family. During this meal one recounts the miracle that occurred and gives thanks to Hashem for His great kindness. [The Alter Rebbe celebrated a Seudas Hodaya for his release from imprisonment of Yud Tes Kisleiv on the 19th of Kisleiv 1801/5561, two years after his release from prison. The Alter Rebbe treated this meal as an absolute obligation, and a Halachic discussion ensued with his brother the Maharil regarding what one is to do if he did not make the Seudas Hodaah on time.]
Seudas Mitzvah: A meal that takes place to commemorate a miracle performed by Hashem is considered a Seudas Mitzvah.
 Shelah; Chavos Yair 70; P”M 444 M”Z 9; Chayeh Adam 155/42; Shulchan Hatahor 219/7; Soles Belula 218/2; Kaf Hachaim 218/9
 I have not found any source in Poskim for this meal being obligatory, and on the contrary the above Poskim all write it is a mere custom. However from the Sefer Hasichos below it is implied that it is an obligation.
 Sefer Hasichos 1940 p. 54-58 [Hebrew], retold by the Rebbe Rayatz in name of Rav Issac Homlir.
 Chavos Yair 70; P”M 444 M”Z 9; Chayeh Adam 154/42 in name of Rashal Baba Kama 37; M”B 697/2
Other Poskim: Some Poskim rule that a Seudas Hodaya is not considered a Seudas Mitzvah. [Peri Chadash 496]