I wanted to understand what this yield does

I wanted to understand what this yield does. In the examples I find, I always see this type of code, but I don't understand what it differs from a normal instance

def get_db():
  db = SessionLocal()
  try:
    yield db
  finally:
    db.close()

This example is in the FastAPI documentation: https://fastapi.tiangolo.com/tutorial/dependencies/dependencies-with-yield/