They used a system of measurement called the Body Mass Index to define words like obese and overweight.

VOA: special.2009.07.21

system is the opposite of the open system, no mass and no energy can flow through the boundary.

孤立系与开系正相反，没有质量或能量,能流过它的边界。

麻省理工公开课 - 热力学与动力学课程节选

But they have really had a big scaling down of the mass transit system this year.

但是今年确实大幅度削减了公共交通。

纽约的公共交通 - SpeakingMax英语口语达人

You just need a few macroscopic variables that are very familiar to you, like the pressure, the temperature, the volume, the number of moles of each component, the mass of the system.

你只需要某些你非常熟悉的宏观变量,比如压强，温度，体积，每个组分的摩尔数，系统的质量。

麻省理工公开课 - 热力学与动力学课程节选

He goes back and redoes the calculation, only in this case he says what I am going to do is I am going to redo the calculation for helium, but I am going to consider not just the mass of the electron but the reduced mass of the system.

他回去重新做了计算，仅在这种情况下他才会说说我将要,为氦重做计算，但我认为,不只是电子的质量,还有系统质量的减少量。

麻省理工公开课 - 固态化学导论课程节选