Map types (or modes) define the style of gameplay a map is. There are currently 3 modes, Objective, Endless, and Holdout.
Objective is the main focus of the game, with the most maps out of the other 2 modes. The main premise of this mode is to escape/fight off zombies whilst doing objectives using teamwork to complete the objectives efficiently and quickly and win. These "objectives" vary differently across all maps. In all objective maps, is a finale, the final set of objectives that are supposed to be tense, difficult, dramatic, and very action packed. Each finale has their own classical song to fit the tone.
Endless is a wave-based mode where your only goal is to kill all zombies each wave, and survive for as long as possible while stationed at a certain area/historical landmark. Beating a wave respawns all dead players. Each wave gets drastically harder, increasing the health of most zombie types and increasing the limit of zombies that can spawn at once. At wave 7+, runners and bombers spawn. Around wave 13+ is when zappers spawn, wave 16+ for cuirassiers, and lastly wave 20+ for igniters. You cannot win in this mode, and it will never end until all players die.
A hybrid between objective and endless. Like endless, you are stuck in a small area, and you must complete an objective in order to win. Currently, there are only 2 maps designated as a holdout map. One is more objective focused, and the other is more endless focused.