As you can see from some examples of shields and their markings, the ways in which a shield may be divided is usually into lines that are either straight or crooked.
Straight lines are carried evenly through the shield and are of four varieties: vertical, horizontal, diagonal dexter, and diagonal sinister. Crooked lines are ones that are carried unevenly through the shield both rising and falling. There are many variations on these basic lines. The main reason why lines are used in heraldry is to differentiate between the various tinctures, charges, or meanings of symbols on the field of the escutcheon itself.
Sometimes the field is divided into a greater number of parts by such lines in order to place on it the arms of several families to which a person may be allied. This is called quartering and may be in many numbers depending on how many divisions one wishes to apply onto the field. Generally however, the division consisted of two equal parts created by a perpendicular line that is called per Pale or by the horizontal line called per Fesse; by the diagonal dexter referred to as per Bend, or by the diagonal sinister, per Bend sinister. A bend is of course a stripe from chief dexter to base sinister – dexter meaning the right side of the shield and sinister to the left - as seen from the viewpoint of the bearer standing behind a shield.