In the science of heraldry, 'sinister' denotes the directional orientation corresponding to the bearer's left. Because a coat of arms is conceptually an extension of the knight’s physical defense, the shield is described from the position of the person holding it. Consequently, the sinister side is viewed on the right by any observer facing the shield. This counter-intuitive spatial terminology is essential for the precise blazoning of armorial bearings and the correct placement of ordinaries and charges.
Historically, the sinister side was often perceived as less honorable than the dexter (right) side due to longstanding cultural and religious associations of the left with ill fortune or secondary status. This distinction is most critically observed in marshaling, particularly when displaying multiple coats of arms on a single shield. For instance, in an impaled shield representing a marriage, the husband’s arms traditionally occupy the dexter half, while the wife’s arms are placed on the sinister, signifying her subordinate legal status under the doctrine of coverture.