Starting from the next map, for simplicity in understanding, events will fall under the following classifications:
Mission - A standard event part of the main story, typically involving a dungeon with one or more bosses at the end, but with some variance.
Ordeal - A shorter event that consists only of an important boss battle(s) as part of the main story, without any sort of dungeon beforehand.
Paralogue - An event unrelated to the main story. Paralogues have no set template and can range anywhere from a Mission format to something entirely unique to it.
Encounter - Similar to an Ordeal, but like a Paralogue is not tied to the main story. Often not scheduled due to how short they are.
Tournament - A unique event type that takes place at the map's designated arena with a slightly different combat system.
Most of these already exist and are nothing new, merely being listed clearly for the first time.
Disclaimer: Only Missions and Ordeals can be listed as a chapter.