Okay kiddo, do you know what a choir is in music? It's a group of singers who sing together, usually in a church. Well, in architecture, a choir is kind of like that, but for buildings!
In a church or cathedral, the choir is usually where the singers stand and sing during a religious service. But in architecture, the choir is the part of the building where the choir singers would stand. And it's not just any part of the building - it's usually the area right behind the altar or the part of the building that sticks out from the rest of the building.
The choir in architecture is usually where the most important religious ceremonies would take place, like a wedding or a baptism. That's why it's often decorated with beautiful sculptures, stained glass windows, and sometimes even mosaics.
So, just like a choir in music, the choir in architecture is an important part where people come together to worship or perform a ceremony.