Definition
Too complex or incomprehensible for someone to understand.
难以理解
The quantum physics lecture was completely over my head; I couldn't understand a thing.
量子物理学讲座完全超出了我的理解范围；我一点也听不懂。
The complex theory he explained went completely over my head; I didn't understand it at all.
他解释的复杂理论完全超出了我的理解范围；我一点也不懂。
When they started talking about technical details, it all went over my head.
当他们开始谈论技术细节时，我完全听不懂。