die Unordnung
mess
A state of untidiness or disorder in which things are not in their place.
In seinem Zimmer herrschte eine schreckliche Unordnung.
There was a terrible mess in his room.

disorder
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mess
A state of untidiness or disorder in which things are not in their place.
In seinem Zimmer herrschte eine schreckliche Unordnung.
There was a terrible mess in his room.

The word is the direct opposite of 'die Ordnung' (order). The prefix 'Un-' is often used in German to form the opposite of a word.
Deine Unordnung auf dem Schreibtisch stört meine Ordnung.
Your mess on the desk disturbs my order.
'Unordnung' (disorder / mess) is often used with the preposition 'in'. The fixed expression 'in Unordnung sein' (to be in disorder) describes the state, while 'etwas in Unordnung bringen' (to put something into disorder / mess something up) describes the action.
Nach der Party war die ganze Wohnung in Unordnung.
After the party, the whole apartment was in a mess.
When talking about an untidy room, typical verbs are 'Unordnung machen' (to make a mess), 'Unordnung hinterlassen' (to leave a mess), or the impersonal phrasing 'es herrscht Unordnung' (there is disorder / a mess).
Bitte mach nicht so eine Unordnung in der Küche.
Please don't make such a mess in the kitchen.
The figurative meaning of 'Unordnung' (disorder) can often be recognized by the adjectives before it. When people speak of 'politischer', 'sozialer', or 'finanzieller' Unordnung (political, social, or financial disorder), it is about chaos in a system, not untidy things.
Die neuen Gesetze führten zu finanzieller Unordnung bei den Kleinunternehmen.
The new laws led to financial disorder among small businesses.
order
'die Ordnung' and 'die Unordnung' are opposites. With 'Ordnung', everything is in its place, or a process follows clear rules. With 'Unordnung', things are scattered around, or a system seems chaotic. In everyday life, both words are often used for rooms, desks, or bags. In broader contexts, 'Ordnung' can also mean an organized system, while 'Unordnung' then describes confusion or chaos.

Die Unordnung im Kinderzimmer ist so groß, dass Max seine Sportschuhe nicht findet.
The mess in the children's room is so bad that Max can't find his sports shoes.
Auf Frau Schwarz' Schreibtisch herrscht immer Ordnung.
Ms. Schwarz's desk is always neat and orderly.