
abgehen
to depart
To leave a place; to move away from a place. Often used for means of transport or people.
Der Bus zum Flughafen geht alle 30 Minuten ab.
The bus to the airport departs every 30 minutes.
to depart / come off
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to depart
To leave a place; to move away from a place. Often used for means of transport or people.
Der Bus zum Flughafen geht alle 30 Minuten ab.
The bus to the airport departs every 30 minutes.

to come off
To detach from something or fall off something it was attached to.
Mir ist ein Knopf von der Jacke abgegangen.
A button came off my jacket.

to go off
Colloquial for: to be really good, generate great excitement, or have a lot of energy.
Die Party gestern Abend ist richtig abgegangen!
The party last night really went off!

what's up?
A colloquial, informal greeting or question about what is happening or going on right now.
Na, was geht ab bei dir so?
So, what's up with you?

to deviate from
To deviate from a path, rule, plan, or topic.
Wir sollten nicht von unserem ursprünglichen Plan abgehen.
We should not deviate from our original plan.

to leave school
To leave a school or educational institution after graduating or early.
Er ist nach der zehnten Klasse vom Gymnasium abgegangen.
He left the Gymnasium after tenth grade.

to be sent
For mail: to be dispatched or sent.
Das Paket ist heute Morgen abgegangen.
The package was sent this morning.
'Abgehen' (to depart / come off) is a separable verb. In a main clause, the prefix 'ab' goes at the end of the sentence. In subordinate clauses and in the infinitive with 'zu', the verb stays together.
Der letzte Zug nach Berlin geht um 22 Uhr ab.
The last train to Berlin departs at 10 p.m.
The perfect tense of 'abgehen' (to depart / come off) is always formed with the auxiliary verb 'sein' because it describes movement or a change of state.
Der Bus ist gerade pünktlich abgegangen.
The bus has just departed on time.
The verb consists of the prefix 'ab-' (away) and 'gehen' (to go). The basic idea that something moves away from or detaches from a point appears in many of its meanings.
Wann geht der nächste Flug nach London ab?
When does the next flight to London depart?
When something unintentionally comes off, the person this happens to is often named in the dative. The thing that comes off is the subject of the sentence.
Beim Essen ist mir ein Stück vom Zahn abgegangen.
While eating, a piece of my tooth came off.
In the meaning 'abweichen' (to deviate), 'abgehen' (to deviate) is always used with the preposition 'von' and the dative.
Wir dürfen nicht vom Thema abgehen.
We must not deviate from the topic.
In an educational context, 'abgehen' (to leave) means to leave a school, often before the regular graduation. Here too, the preposition 'von' is used.
Sie ist nach der 11. Klasse von der Schule abgegangen, um eine Ausbildung zu machen.
She left school after 11th grade to do vocational training.
The meaning 'großartig sein' (to be great) is purely colloquial. It is used for parties, concerts, or other high-energy events.
Das Konzert gestern war der Hammer, die Band ist total abgegangen!
The concert yesterday was awesome; the band totally went off!
'Was geht ab?' (what's up?) is a fixed, very informal greeting among friends, similar to 'Was ist los?' (what's going on?) or 'Wie geht's?' (how are you?).
Hey, lange nicht gesehen! Was geht ab?
Hey, long time no see! What's up?
to set off / start
Losgehen and “Was geht ab?” can refer to an event. Losgehen asks or says when something begins, while “Was geht ab?” is an informal way of asking what is happening or going on right now. Use losgehen for the start and “Was geht ab?” for an informal question about the situation as it unfolds.

Weißt du, was bei dem Konzert heute Abend abgeht?
Do you know what's going on at the concert tonight?
Weißt du, wann das Konzert heute Abend losgeht?
Do you know what time the concert starts tonight?