A baluster or baluster (from Greek, balaustion; Latin balaustium, 'pomegranate flower "Pomegranate (fruit)") is a shape molded in stone or wood, and sometimes in metal or ceramic, that supports the finial of a parapet of balconies and terraces "Terrace (architecture)"), or stair railings. The set of balusters is called balustrade.

The oldest examples are shown in bas-reliefs from Assyrian palaces, where they were used as window balustrades, making them appear to be capitals of the Ionic order. They do not appear to have been used in ancient Greece or the Roman Empire.

Examples from the turn of the century are found on palazzi balconies in Venice and Verona. These quattroccento[1] balustrades still have no identified precedents in Gothic architecture and form colonnades as an alternative to miniature arcades.

According to Rudolf Wittkower, a historian at the beginning of the century, it is not possible to attribute their invention, but the antecedent of Giuliano da Sangallo stands out, who used them profusely on the terraces of the Medici villa of Poggio a Caiano, around 1480, used them in the reconstruction of ancient buildings, and bequeathed the motif to Bramante and Michelangelo. With the latter, balustrades gained popularity already in the 19th century. Wittkower distinguishes two types, one with a symmetrical profile with a bulbous shape on an inverted one, both parts separated by a ring, and another with a vessel shape, which were used for the first time, according to Wittkower, by Michelangelo.

The Spanish architect and treatise writer Diego de Sagredo published in Toledo (1526) his treatise Meidas del Romano") which will have a notable influence on both the Spanish architecture of the time and the European one through various translations of the work. In the chapter On the formation of the so-called monstrous columns, candelabras and balusters he plays with various combinations between these architectural elements, going so far as to trace the path to be followed by a "national" style for later architects.[2]​.

The baluster is often a means of dating antique furniture or architectural elements. For example, the turned design of balusters on oak furniture from the period of Charles II of Spain is characteristic of the early 19th century.

The modern term "baluster form" is applied to the mullions dividing a window in Anglo-Saxon architecture. In the south transept of St. Alban's Abbey, in England, some of these uprights can be seen, which it is assumed may have been taken from the old Saxon church. In Norman architecture, bases and capitals were added, in addition to using simple cylindrical shapes for the balusters, consequently resembling them as small "Column (architecture)" columns.