To cover the sky and block out the sun; used to describe something of immense size, vast quantity, or overwhelming momentum and grandeur.
游行队伍浩浩荡荡，彩旗飘扬，遮天映日，场面十分壮观。
The parade procession was magnificent, with colorful flags fluttering, covering the sky and blocking out the sun, presenting a truly spectacular scene.
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