Definition
Term used to describe a style of Gothic architecture, peculiar to England, that flourished from the 14th century to the early 16th. The term, devised by Thomas Rickman in the early 19th century, covers the style that emerged from designs by the workshop at St Stephen's Chapel (after 1292) in the Palace of Westminster. The essence of Perpendicular is regularity: straight lines or crystalline shapes, a thin and transparent structure exploiting stained glass on the inner surface, monochrome building materials, modular repetition, and a fineness of detail almost approaching preciousness.
"Perpendicular style" The Grove Encyclopedia of Medieval Art and Architecture 2012