das Ereignis
event
Something that happens; an incident or process that often has special significance.
Die Wiedervereinigung Deutschlands war ein historisches Ereignis.
The reunification of Germany was a historic event.

event
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event
Something that happens; an incident or process that often has special significance.
Die Wiedervereinigung Deutschlands war ein historisches Ereignis.
The reunification of Germany was a historic event.

'Das Ereignis' (the event) is the noun corresponding to the verb 'sich ereignen' (to occur/happen), which means 'geschehen' (to happen) or 'passieren' (to happen). The ending '-nis' is often used to form nouns from verbs.
Gestern hat sich ein schwerer Unfall auf der Autobahn ereignet.
Yesterday, a serious accident occurred on the highway.
'Ereignis' (event) is often used for important or special occurrences. Typical adjectives are 'historisch' (historic), 'politisch' (political), 'persönlich' (personal), 'freudig' (joyful), or 'tragisch' (tragic).
Die Geburt ihres Kindes war ein freudiges Ereignis für die ganze Familie.
The birth of their child was a joyful event for the whole family.
You can recognize the technical meaning in computer science from words such as 'auslösen' (to trigger), 'Mausklick' (mouse click), 'Tastendruck' (keystroke), or 'Programm' (program).
Jeder Tastendruck auf der Tastatur löst ein bestimmtes Ereignis aus.
Each keystroke on the keyboard triggers a specific event.
story / history
'die Geschichte' and 'das Ereignis' can both mean something that happened. 'das Ereignis' is a single event, often something special or important. In this colloquial meaning, 'die Geschichte' refers more to the whole matter or affair, with its course of events, its details, and sometimes also problems. The words can be confused because an event can be part of a Geschichte. If you just want to say that something happened, 'Ereignis' fits. If you mean the whole situation or the complicated course of events, 'Geschichte' fits better.

Das Konzert im Park war für viele Kinder ein besonderes Ereignis.
The concert in the park was a special event for many children.
Die Geschichte mit dem kaputten Auto hat uns den ganzen Urlaub beschäftigt.
The whole affair with the broken-down car occupied us for the entire vacation.