Movement Rate of "12" means:

Non Combat Movements:

Slow Walk, 20' / minute (searching for traps, this would probably be your typical dungeon, sewer pace. This is also the only one I can see having any bearing on the game, but the others fit with this one as a base.)

Normal Walk, 60' / minute (dungeon crawl, looking for hidden doors etc, being careful, but not looking for traps)

Steady Walk, 120' / minute (no looking for traps, hidden doors, etc, a place where you feel pretty confident, and are just going from point a to point b)

Fast Walk/Run, 240' / minute (Penalties on surprise, AC, etc, your fastest movement rate, getting out for example)

Melee Movements:

Running 240' /minute (no dex bonus to AC, +1 penalty to AC, this is your basic running at double your movement rate)

Normal 120' /minute (no attacking or defending, you get your normal AC, and can go this far in a normal combat round as per the DMG section on combat, this is a normal 1 round action)

Retreating, 40' / minute (defending only)

Fighting/Spellcasting 10' / minute (attacking and defending, casting a spell, maintaining a spell that needs concentration)

Outside/Overland Movement:

This will generally not have any bearing on the group, as you are limited to the movement rate of the War Horses which is 15 for travel. So that is 30 miles a day.  Normal overland movement is double your movement rate in miles.

Normal Walk, 120' / minute
Steady Walk/Marching, 180' / minute
Fast Walk/Forced March, 240' / minute

Learning New Spells:

Spell Learning: 1 new spell every 2 days while at rest, 1 new spell each week while travelling. This is for spells that the PC has access to, not for researching a new spell.