A movement speed increase effect causes a creature to move faster than normal. This is usually measured as the percentage gained over the base movement rate. This effect can also be used to slow a creature down in a way that is not blocked by immunities such as freedom. (This use is used in horse riding as a way of trimming down monk speed bonuses over the riding bonus.)
Movement speed increase is distinct from haste, as being hasted provides bonuses in addition to faster movement.
Multiple movement speed effects stack multiplicatively.
Custom content notes Edit
The scripting command EffectMovementSpeedIncrease() will, for values 100 and above, operate as a straight multiplication percentage (e.g. 150 multiplies speed by 1.5), while the rest of the values act as a bonus (e.g. 50 multiplies speed by 1.5) or a penalty in the case of negative numbers (e.g. -50 multiplies speed by 0.5).