The yellow element on the flag of Brazil is a rhombus. It is the large four-sided yellow figure set against the flag’s green field, with the blue celestial globe placed inside it.
A rhombus is a quadrilateral whose four sides have equal length. In everyday descriptions, people sometimes call Brazil’s yellow shape a diamond because it is tilted like one, but “rhombus” is the more precise geometric term. A square is a special type of rhombus, yet Brazil’s yellow figure is not a square because its angles and proportions are different.
The yellow rhombus and green field were carried over, with modifications, from the flag of the Empire of Brazil. The republican flag was officially adopted on November 19, 1889, after Brazil became a republic. The central blue disk represents the sky over Rio de Janeiro on the morning the republic was proclaimed.
Today the disk contains 27 white stars, representing Brazil’s federal units, and a curved band bearing the motto “Ordem e Progresso,” or “Order and Progress.” The yellow rhombus remains the visual frame that separates this celestial design from the green background.