Short answers, pulled from the story.
Architecture is the study and practice of designing structures, especially habitable ones. It uses civil engineering techniques but is considered a visual art, covering the process and product of sketching, conceiving, planning, designing, and constructing buildings.
According to the Roman architect Vitruvius, a good building should satisfy firmitas, utilitas, and venustas, meaning durability, utility, and beauty. He set them out in De architectura, the earliest surviving text on architectural theory, written in the early 1st century BC.
Louis Sullivan, a 19th-century architect of skyscrapers, declared that form follows function. The idea introduced function in place of Vitruvius' utility, expanding it to cover practical, aesthetic, psychological, and cultural dimensions of a building.
Modern architecture began as an avant-garde movement immediately after World War I. It sought a new style for a post-war social and economic order, reducing buildings to pure forms, removing ornament, and exposing steel beams and concrete surfaces.
Modernism stripped buildings of historical references and ornament in favor of simplified geometric forms, leading to the International Style. Postmodernism reacted against that austerity, combining contemporary technology with older aesthetics. Robert Venturi defined postmodern architecture as a decorated shed.
Architecture includes residential, commercial, industrial, landscape, and interior architecture, along with urban design. Other branches include naval architecture, the engineering design of marine vessels, and seismic or earthquake architecture, a term introduced in 1985 by Robert Reitherman.