Hello, I need some clarifications on The Lid-Driven Cavity Problem.

What does it actually mean? I know cavities are bubbles created when a fluid moves through liquid in low pressure zones, but does the Lid-Driven cavity take the bubble to be of a square cavity? And the lid is the upper part of the square, where the other three sides are no-slip conditions, correct?\

I also need help on what the:

initial conditions

boundary conditions

free slip + no-slip boundary conditions

and how to non-dimensionalize the Navier-Stokes equations.