It doesn't have to be a real container to contain it it's just an imaginary boundary there.

它不必是，一个真实的容器，只是一个想象的边界。

youdao

The method of solving the implicit scheme of difference equations by means of imaginary boundary condition was proposed.

提出了应用“假想边界”求解数学模型的隐式差分格式的方法。

youdao

The area is filled if the number of boundary lines going in one direction (relative to the imaginary line) is not equal to the number of boundary lines going in the other direction.

如果朝一个方向(相对于想象的线)的边界线的数量不等于朝其它方向的边界线的数量，那么该区域是已填充的。

youdao

It doesn't have to be a real container to contain it It's just an imaginary boundary there.

它不必是,一个真实的容器,只是一个想象的边界。

麻省理工公开课 - 热力学与动力学课程节选

"Feathers are one of the things that transit the imaginary boundary we put between the human and natural world, " he explained.

WSJ: Of Feathers, Showgirls and Biology