zusammenkommen
to come together
To meet or gather in one place.
Die ganze Familie ist zu Weihnachten zusammengekommen.
The whole family came together for Christmas.

to come together
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to come together
To meet or gather in one place.
Die ganze Familie ist zu Weihnachten zusammengekommen.
The whole family came together for Christmas.

'Zusammenkommen' (to come together) is a separable verb. The prefix 'zusammen-' goes to the end in a main clause. In subordinate clauses and in the infinitive with 'zu', the verb stays together.
Morgen kommt der Vorstand zu einer wichtigen Sitzung zusammen.
Tomorrow the board is coming together for an important meeting.
Since 'zusammenkommen' (to come together) describes movement or a change of state, the perfect tense is always formed with the auxiliary verb 'sein' (to be), not with 'haben' (to have).
Letzte Woche sind wir im Park zusammengekommen.
Last week we came together in the park.
The subject of the sentence reveals the meaning: if it is people, it is about a meeting. If it is money or an amount, it is about accumulation. If it is two people, it can mean a romantic relationship. If it is circumstances, they occur at the same time.
Bei dem Projekt kamen viele Probleme zusammen.
Many problems came together in the project.
When referring to money or other amounts, 'zusammenkommen' (to come together) describes the result of a collection. The source is often named with 'bei' (at/during) or 'durch' (through).
Beim Kuchenverkauf in der Schule sind 200 Euro zusammengekommen.
At the cake sale at school, 200 euros came together.
In colloquial language, 'zusammenkommen' (to get together) is a very common way to say that two people have become a couple.
Wusstest du, dass Anna und Paul zusammengekommen sind?
Did you know that Anna and Paul got together?
to meet / to hit
'treffen' and 'zusammenkommen' can both describe several people being in one place. 'treffen' is often used when two or more people have arranged to meet or encounter one another. 'zusammenkommen' puts more emphasis on the group or on gathering in one place. It works well for teams, families, clubs, or meetings. In many situations, both are possible, but they do not sound exactly the same: 'Ich treffe Tom' sounds personal. 'Das Team kommt zusammen' sounds more like a group gathering.

Am Montag kommt das ganze Team zu einer kurzen Besprechung zusammen.
On Monday, the whole team is coming together for a short meeting.
Im Sommer treffen wir unsere Nachbarn oft im Garten.
In summer, we often meet our neighbors in the garden.