In additon, this glossry of terms is helpful from here.
Definition
of terms
Plié [plee-AY]
Bent,
bending. A bending of the knee or knees. This is an exercise to render the joints and muscles soft and pliable and the tendons flexible and elastic, and to develop a sense of balance. There are two principal pliés: grand plié or full bending of the knees (the knees should be bent until the thighs are horizontal) and demi-plié or half-bending of the knees. Pliés are done at the bar and in the centre in all five positions of the feet. The third position is usually omitted. When a grand plié is executed in either the first, third or fourth position croisé (feet in the fifth position but separated by the space of one foot) or the fifth position, the heels always rise off the ground and are lowered again as the knees straighten. The bending movement should be gradual and free from jerks, and the knees should be at least half-bent before the heels are allowed to rise. The body should rise at the same speed at which it descended, pressing the heels into the floor. In the grand plié in the second position or the fourth position ouverte (feet in the first position but separated by the space of one foot) the heels do not rise off the ground. All demi-pliés are done without lifting the heels from the ground. In all pliés the legs must be well turned out from the hips, the knees open and well over the toes, and the weight of the body evenly distributed on both feet, with the whole foot grasping the floor.
Foot Positions
First position (Première position):In this position the feet form one line, heels touching one another.
Second position (Seconde position): The feet are on the same line but with a distance of about one foot between the heels.
Third position (Troisième position): In the third position one foot is in front of the other, heels touching the middle of the other foot.
Fourth position (Quatrième position): In the fourth position the placement of the feet is similar to that in the third position, the feet being parallel and separated by the length of one foot. This is the classical fourth position but it may also be done with the feet in the first position, only separated by the space of one foot. The former is known as quatrième position croisée (crossed fourth position), while the latter is called quatrième position ouverte (open fourth position). Today quatrième position croisée is done with the feet placed as in the fifth position, parallel and separated by the length of one foot, instead of the third position.
Fifth position (Cinquième position):In the fifth position, Cecchetti method, the feet are crossed so that the first joint of the big toe shows beyond either heel. In the French and Russian Schools the feet are completely crossed so that the heel of the front foot touches the toe of the back foot and vice versa.
of the knee or knees. This