ultra
Expresses an extreme intensification; means 'very', 'extremely', or 'excessively'. It is often used colloquially.
Die Party gestern war ultra cool.
The party yesterday was ultra cool.

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Expresses an extreme intensification; means 'very', 'extremely', or 'excessively'. It is often used colloquially.
Die Party gestern war ultra cool.
The party yesterday was ultra cool.

In the meaning of 'sehr' (very) or 'extrem' (extremely), 'ultra' belongs to youth language and colloquial speech. It is usually avoided in formal or written contexts.
Das neue Videospiel ist ultra schwer.
The new video game is ultra hard.
As an intensifier, 'ultra' stands directly before the adjective or adverb that it intensifies. It is not declined, so its form does not change.
Der Film war ultra spannend.
The film was ultra exciting.
If 'ultra' appears before an adjective like 'gut' (good) or 'schnell' (fast), it means 'extremely'. In the context of sports and fans, often as a noun ('die Ultras') or in words like 'Ultra-Szene' (Ultra scene), it refers to fanatical supporters.
Das Konzert war ultra laut.
The concert was ultra loud.
very
'sehr' and 'ultra' can both make a quality stronger. 'sehr' is neutral and suitable in almost any situation. 'ultra' means more like 'extremely' or 'very strongly', but it sounds colloquial and modern. It works well in casual conversations, for example 'ultra teuer' (ultra expensive) or 'ultra schnell' (ultra fast). In formal situations, at work, or in exams, 'sehr' usually sounds more natural and safer.

In der Pause finde ich den neuen Stundenplan ultra kompliziert.
During the break, I find the new class schedule ultra complicated.
Der Zug ist vor dem Termin sehr voll.
The train is very crowded before the appointment.