to describe something correctly and thoroughly, and to say what standards, limits, qualities etc it has that make it different from other things

确定，说明，界定:

the ability to define clients' needs

确定客户需求的能力

The duties of the post are difficult to define.

这一职位的职责很难界定。

The tasks will be clearly defined by the tutor.

这些任务将由导师来说明。

70% of the workers can be defined as low-paid.

70% 的工人可以被划定为低收入者。

to explain exactly the meaning of a particular word or idea

给…下定义，解释;

I'll now try to define the term 'popular culture'.

我现在来试试给“通俗文化”这个词下定义。

A budget is defined as 'a plan of action expressed in money terms'.

“预算”一词定义为“以金钱来表述的行动计划”。

Define precisely what you mean by 'crime'.

把你说的“犯罪”明确定义说明一下。

to show the edge or shape of something clearly

标明…界限，明确显出…轮廓;

The bird has sharply defined black and rust markings.

这只鸟长着鲜明的黑色和铁锈色斑点。