AIM Clarity

Gotta hand it to the writers of the Airman's Information Manual. I was breezing through (a little light reading) and came across this passage:

Friction is defined as the ratio of the tangential force needed to maintain uniform relative motion between two contacting surfaces (aircraft tires to the pavement surface) to the perpendicular force holding them in contact (distributed aircraft weight to the aircraft tire area). Simply stated, friction quantifies slipperiness of pavement surfaces.

I'm not sure what "slipperiness" means, but the first part is crystal clear.