der Horror
nightmare / horror
Colloquial for an extremely unpleasant, stressful, or terrible situation or experience.
Die Wohnungssuche in dieser Stadt ist der absolute Horror.
Looking for an apartment in this city is an absolute nightmare.

horror
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nightmare / horror
Colloquial for an extremely unpleasant, stressful, or terrible situation or experience.
Die Wohnungssuche in dieser Stadt ist der absolute Horror.
Looking for an apartment in this city is an absolute nightmare.

When 'Horror' (nightmare / horror) describes a terrible experience, the word is used colloquially. It expresses a strong, often exaggerated negative emotion about a situation.
Die lange Wartezeit beim Amt war der reine Horror.
The long wait at the government office was pure horror.
In the colloquial meaning, 'Horror' (nightmare / horror) is often intensified with adjectives such as 'der pure Horror' (pure horror) or 'der absolute Horror' (an absolute nightmare) to describe the situation as extremely negative.
Jeden Morgen im Stau zu stehen, ist für mich der absolute Horror.
Being stuck in traffic every morning is an absolute nightmare for me.
To describe the feeling of shock, 'Horror' (horror) is often used with the preposition 'vor' to indicate the cause of the fear. The pattern is: 'vor Horror' + verb, e.g. 'schreien' (to scream), 'erstarren' (to freeze).
Sie erstarrte vor Horror, als sie die Gestalt im Fenster sah.
She froze in horror when she saw the figure in the window.
As a genre label, 'Horror' (horror) is often the first part of compound nouns. Typical examples are 'der Horrorfilm' (horror film), 'die Horrorgeschichte' (horror story), or 'der Horrorroman' (horror novel).
Ich lese gerne Horrorbücher, aber ich schaue nicht gerne Horrorfilme.
I like reading horror books, but I don't like watching horror films.
fear
'die Angst' and 'der Horror' can both describe a very unpleasant feeling. 'Angst' is the normal word when you feel threatened or are afraid of something. 'Horror' is stronger and often more dramatic. It can mean a feeling of great shock, but also, colloquially, a very bad or stressful situation. Learners may confuse the words because both have to do with fear. As a practical rule: for the feeling, you usually use 'Angst'. 'Horror' fits better when something was extremely terrible or when you want to exaggerate strongly.

Der erste Arbeitstag im Supermarkt war für Lena der Horror, weil die Kasse ständig nicht funktionierte.
Lena's first day working at the supermarket was a nightmare because the cash register kept not working.
Vor dem Gewitter im Wald hatte Herr Neumann am Wochenende große Angst.
Mr. Neumann was very afraid of the thunderstorm in the forest over the weekend.