der Chor
choir
A group of people who sing together.
Meine Tochter singt im Schulchor.
My daughter sings in the school choir.

choir
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choir
A group of people who sing together.
Meine Tochter singt im Schulchor.
My daughter sings in the school choir.

You can recognize the meaning of 'Chor' (choir/chorus) from the verb: 'im Chor singen' (to sing in a choir) refers to the group, 'einen Chor singen' (to sing a chorus) refers to the piece of music, and 'im Chor stehen' (to stand in the choir) refers to the part of the church.
Er singt seit fünf Jahren im Kirchenchor.
He has been singing in the church choir for five years.
'Chor' (choir) is a common component of compound nouns that describe the type of singing group more precisely. This makes it easy to recognize what kind of choir it is.
Der Kinderchor hat morgen seinen großen Auftritt.
The children's choir has its big performance tomorrow.
The most common and important combination is 'im Chor singen' (to sing in a choir). The preposition 'in' with the dative expresses belonging to the group.
Singen Sie gerne? Dann kommen Sie doch in unseren Chor!
Do you like singing? Then come join our choir!
orchestra
'der Chor' and 'das Orchester' both belong to music and often perform together in concerts. The important difference is: a choir consists of people who sing. An orchestra consists of musicians who play instruments. The words can be confused because both groups make music and are often led by a conductor or director. When voices are the focus, you say 'Chor'. When instruments are the focus, you say 'Orchester'.

Am Sonntag singt der Chor ein neues Lied in der Kirche.
On Sunday, the choir sings a new song in the church.
Das Orchester spielt vor der Oper eine kurze Ouvertüre.
Before the opera, the orchestra plays a short overture.