Condition

Certain effects apply a condition to its target(s). Conditions are usually temporary, harmful and require certain actions to be taken in order to remove them sooner.

If more than one condition affects a character, they are all applied. Certain effects can’t be combined, thus the most severe effect supersedes the others.

Conditions are not magical effects by themselves but they can be bestowed by a magical effects, like spells and weapon effects.

Removing
Although death is a condition itself, it usually removes most of the other afflicting conditions.

Usually removing the source that applies the condition removes also the condition but not always. e.g. Removing the disease blinding sickness does not remove the condition blinded it might cause.

The easiest ways to remove (some) conditions are restoration, heal, panacea, and similar effects. Resting and simply waiting for the duration to wear off also works.

The only condition that can be removed without magical aid or by resting is invisibility.

Complete list of conditons in DDO
Category:Conditions

Environments effects
Some quests and areas occur in a special environment that changes the rules how your character behaves. Like most conditions, environmental effects often appear on your buff bar. Unlike conditions, environmental effects cannot be removed, unless you leave the location. See Environmental effects.

PnP Dungeons and Dragons
Unlike in DDO, conditions in PnP D&D are permanent. Only if something specially states its removes a certain condition, only then the condition is removed.

Some conditions are missing from DDO, like confused, grappling, staggered and flat-footed to name a few.

Some are working only partially, like frightened, stunned and energy drained to name a few.

Some conditions are combined, like all states of fear instead of Cowering, Frightened, Shaken