It means that for pressure-sensitive applications mouse or touch input behaves as if the stylus was used with moderate pressure. Which makes sense if you consid

It means that for pressure-sensitive applications mouse or touch input behaves as if the stylus was used with moderate pressure. Which makes sense if you consider something like a drawing application where the pressure makes the brush larger. You neither want no brush at all (0 pressure), nor something blown out of proportion (1) but rather what is similar to when using a pen normally. (Full pressure for a stylus is usually a lot of force that's rarely, if ever, used.)