Toe In / Toe Out describes the angle of the front (or rear) tires when viewed from above (see pictures). If the front of the tires angles in (or towards the chassis), that is Toe In. If the front of the tires angles out (or away from the chassis), that is Toe Out.
Toe can be adjusted to increase or decrease steering and steering response. You adjust Toe by turning the turnbuckles (if equipped) attached to the steering knuckles or hub carriers.
Adding Toe In will decrease steering into a corner, but add steering out during acceleration. Toe In will also stabilize the car under acceleration. Toe Out will increase steering into a corner, but cause the car to wander a little on the straights and bumpy sections.
Adding Toe In results in less on-power steering and slightly more entering a corner. Less Toe results in more on-power steering and slightly less entering a corner. Less Toe will also increase straightaway speed.