文化是一个非常难讲清楚的概念。

Culture is a difficult concept to pin down.

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这本书使你对古希腊生活有个清楚的概念。

This book gives you a good idea of life in ancient Greece.

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仔细想来，风寒是一个定义不清楚的概念。

If we think about it, wind chill is an ill-defined concept.

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The second question that you might think we'd want to get clear on is, "What's the idea, or what's the concept, of surviving?"

第二个你要,弄清楚的问题是,活着的概念是什么

耶鲁公开课 - 死亡课程节选

The second law is going to define entropy, and is going to tell us about the direction of time, something that conceptually we, clearly, understand but is going to put a mathematical foundation on which way does time go.

第二定律定义了熵，它告诉我们,时间的流向，虽然我们清楚地,知道这个概念,但还是要为时间流动的方向,建立一个数学基础。

麻省理工公开课 - 热力学与动力学课程节选