die Überraschung
surprise
An unexpected event, piece of news, or gift.
Die Party war eine gelungene Überraschung für ihren Geburtstag.
The party was a successful surprise for her birthday.

surprise
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surprise
An unexpected event, piece of news, or gift.
Die Party war eine gelungene Überraschung für ihren Geburtstag.
The party was a successful surprise for her birthday.

'Die Überraschung' (the surprise) is the noun related to the verb 'überraschen' (to surprise). If you know the verb, you can easily derive the meaning of the noun, and vice versa.
Er wollte seine Freundin mit einer Reise nach Paris überraschen.
He wanted to surprise his girlfriend with a trip to Paris.
When referring to an event, 'Überraschung' (surprise) is often combined with adjectives like 'gelungen' (successful), 'böse' (nasty), 'schön' (nice), or 'groß' (big). Typical verbs are 'vorbereiten' (to prepare), 'planen' (to plan), or 'erleben' (to experience).
Seine Abschiedsfeier war eine wirklich gelungene Überraschung.
His farewell party was a truly successful surprise.
To express the feeling of astonishment, the fixed expression 'zu meiner/deiner/seiner Überraschung' (to my/your/his surprise) is often used. It usually appears at the beginning of the sentence.
Zu meiner großen Überraschung hatte er das ganze Haus allein aufgeräumt.
To my great surprise, he had cleaned up the whole house by himself.
miracle / wonder
'das Wunder' and 'die Überraschung' both have to do with something unexpected. A 'Überraschung' can be big or small: a gift, a piece of news, or an unexpected visit. A 'Wunder' is much stronger. You use it when something seems almost impossible, is inexplicable, or is especially amazing and fortunate. Learners may confuse the words because both describe something unexpected. As a practical rule: for normal unexpected things, 'Überraschung' fits better; for something very special or barely explainable, you are more likely to say 'Wunder'.

Zum Geburtstag wartete eine schöne Überraschung auf dem Küchentisch.
For the birthday, a lovely surprise was waiting on the kitchen table.
Nach dem schweren Unfall war es ein Wunder, dass niemand verletzt wurde.
After the serious accident, it was a miracle that no one was injured.