in concert idiom
（一同）演出
playing or singing with other musicians in a public performance
She was appearing in concert at Carnegie Hall. 她参加了在卡耐基音乐厅的演出。
formal共同，一起；一致
together
If the member countries would act in concert, the problem might be solved more easily. 如果成员国行动一致，这个问题可能会更容易解决。