This is an ill-defined concept.

这是一个不确切的概念。

An ill-defined concept;

一个定义不明的概念；

Was that an attempt to define an ill-defined enemy?

那是不是故意对敌人的丑化？

It may be vague and ill-defined to our conscious gaze.

这幅图画可能是模糊的，也可能被我们自己的意识错误定义。

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

仔细想来，风寒是一个定义不清楚的概念。