What it means is if you'd release a rock at that location one second before with a certain speed that we can calculate, it would've ended up here with precisely the position and velocity it had at the beginning of our experiment.

它的意义在于,若在该处以特定速度抛出一个物体,这个速度可通过计算得到,一秒之后,物体会运动至我们设定的起点,并且速度为我们设定的初速度

耶鲁公开课 - 基础物理课程节选