A leg's motion has four phases, beginning with the foot on the ground. Then the foot lifts, moves through the air, and returns to the ground again. Biped divides this motion into four phases as follows:
Touch occurs at the leg keyframe where the leg's foot first touches the ground and always corresponds with the start frame of a footstep in Track View.
Plant occurs after touching, and before lifting. It is always in between the start and end frames of a footstep in Track View.
Lift occurs at the keyframe where the leg's foot lifts off the ground and always corresponds with the end frame of each footstep in Track View.
Move occurs while the foot is in the air and is always in the intervals in between steps in Track View. In walking, while one foot moves the body is supported by the other leg. In running or jumping, while a foot moves there is a period where the body is not supported, and moves in midair.