And in the plane there is some other object.

在平面上有一个物体

耶鲁公开课 - 基础物理课程节选

Um-hmm. So, it's going to be the y z nodal plane, or in other words, we can say it's any place where phi is equal to 90 degrees.

嗯，是ｙｚ平面，换句话说，是在phi等于９０度的面。

麻省理工公开课 - 化学原理课程节选

Then, I gave you one other very important example of a particle moving in the x-y plane.

下面我再拿一个重要的例子,质点在 x-y 平面内的运动

耶鲁公开课 - 基础物理课程节选