Refers to a style of architecture dependent on exposed rough concrete as structural form, particularly dating to the 1960s and 1970s, but which is allied to the late works of Le Corbusier, which itself was characterized by raw concrete and undisguised functional features. The term originated from the French béton brut, or 'raw concrete.'

Source: AAT

http://vocab.getty.edu/page/aat/300112048