the.com/brownstone

means A terraced townhouse — classically in a city like New York — faced in reddish-brown sandstone, with a flight of stoop steps leading up to the main entrance.

from The word simply names its material: a brown sandstone (often quarried in the Connecticut River valley and nearby regions) that 19th-century builders sliced into slabs and bolted onto row house facades as a cheap, fashionable veneer over plainer brick. The stone became so synonymous with the look of blocks in Brooklyn, Manhattan, and Boston that by the later 1800s 'brownstone' stopped meaning just the rock and started meaning the whole building — stoop, cornice, and all.