Fast travel is a generic category of all methods that accelerate movement from A to B.
Games which disallow fast travel by any means, force player to walk/run long distance(aka "running simulator").
Fast travel that is unrestricted allows the most freedom of movement at expense of immersion and content segregation.

General types:

1.NPC transport service from A to B. Temporary vehicle/mount is often provided as visual to obscure load time.
2.Portals/Entrance/Shortcut: Player enter a one-way or two-way portal to travel to destination.
3.Teleport beacon/Waypoint: player selects a destination from a list. Most versatile.
4.NPC interaction: player asks NPC for travel to B. Typically restricted to towns/quests.
5.Dedicated Travel skill that transports player to a map location. usually there is requirement that player visited the area beforehand.

Games which disallow fast travel usually have:
Poor man "fast travel"(doesn't provide immediate transportation):
1.Mounted/Vehicle travel: player enters his vehicle/object/being to travel significantly faster.
2.Long-range teleport/phasing skill that can be used repeatedly to skip around the area.
3.Character speed increment: by buffs/skills/items. By stacking the runspeed modifiers characters can travel as fast as mounts, shortening time from A to B.