Basal slip or sliding as it's often called, basically refers to the slipping or sliding of a glacier across bedrock, actually across a thin layer of water on top of the bedrock.

底部滑移，也通常被称为滑动，大致指的是冰川在基岩上的滑动，实际上是在基岩上部的一层薄薄的水上的滑动。