Hard edge: Hard-edge painting consists of rough, straight edges that are geometrically consistent. It encompasses rich solid colors, neatness of surface, and arranged forms all over the canvas. Can be seen as a subdivision of Post-Painterly Abstraction, which in turn emerged from Colour Field painting. The term was coined by the Californian critic Jules Langster in 1959 to describe those abstract painters, particularly on the West Coast, who in their reaction to the more painterly or gestural forms of Abstract Expressionism adopted a particularly impersonal paint application and delineated areas of colour with particular sharpness and clarity. This kind of approach to abstract painting became extremely widespread in the 1960s.
Hudson River School: The Hudson River School was a mid-19th century American art movement by a group of landscape painters, whose aesthetic vision was influenced by romanticism. Their paintings depict the Hudson River Valley and the surrounding area, as well as the Catskill Mountains, Adirondack Mountains, and White Mountains of New Hampshire. Note that "school" in this sense refers to a group of people whose outlook, inspiration, output, or style demonstrates a common thread, rather than a learning institution.