There are many nouns that describe an event, occation, or happenings
They all can be translated to either;
* der Anlass
* das Geschehen
* das Geschehnis
* das Ereignis
* die Veranstaltung
How do I know which one I should choose?
Literally this is "the reason" (for an event), not the event itself.
Example: At the party the project's leader says:
Translation: "The Reason for out meeting is the completion of the project. This is what we want to celebate now."
Literally this is "the happening".
Translation "Erwin was in the restaurant by accident. From his place at the bar he watched the event."
This is bad German, nobody uses this word. Forget it. Use »das Geschehen« instead.
This is, what best matches to "the event". It can be a planned event or an event that happens by accident.
Translation: "Nasa is panning to ignite a rocket tomorrow. I already noted this event in my calendar.
Translation: "The event that triggered the tsunami was an earthquake."
This is a planned event that must be prepared and where people meet. This can be a music-gig, a party, a play in a theater, a political demonstration or something similar.
Translation: "80.000 visitors are expected to the event in the banquet hall."
(can be used in both forms: maskulin and neuter; both have the same meaning)
We use the english word "Event" as a foreign word in german sentences. (In German kontext you must use uppercase letter for the first letter because it is a noun.) But the meaning is not exactly the same as the english original. The english original fits best to »das Ereignis«, not to »das Event«!
We use »das Event« more as a synonym to »die Veranstaltung«.
So you can say this in German:
"Only 50.000 Visitors came to the event in the big hall."
But this is a wrong usage of »das Event«:
Use »das Ereignis« instead:
Translation: "The event, that killed the man was the explosion of a bomb."