An arch buttress, or simply buttress (from the French arc-boutant, literally arch that transmits),[1]​ is an exterior structural element in the shape of a half arch "Arch (construction)") that collects the pressure at the start of the vault and transmits it to a buttress, or abutment, attached to the wall of a side nave. It is a distinctive construction element of Gothic architecture, along with the pointed arch and the ribbed vault.

As an external discharge arch, it is usually in an inclined position; It is, therefore, a rampant arch or tranquil arch, since it has its beginnings at different heights. The flying buttress is part of the Gothic structure, but can only be seen from the outside. The lower part rests on a stirrup, buttress, or buttress; and the upper part generally supports a ribbed vault. A pinnacle (called a spire when it is very high) crowns the abutment, decorating it, and helping with its weight to the stability of the structure.

It was used for the first time in 1180 in the construction of the central nave of Our Lady of Paris, to reinforce its pointed vault. Through this system, it was possible to transmit the pressures from the start of the high vaults to the exterior buttresses, allowing larger openings to be opened in the walls of the central nave. With the pointed arch, thanks to its verticality, the height of the building was raised.

This system replaced the stirrups used in the Romanesque to counteract the lateral thrusts of the vault. By freeing the wall from the buttress function, they could be made taller and more slender, allowing light to enter through the stained glass windows. Later, and in order to prevent the displacement of the buttresses due to the thrust of the buttresses and, in turn, contribute to the ascending effect of Gothic architecture, they were crowned with a pinnacle or pillar finished in a pyramidal shape "Pyramid (geometry)") at the top. The flying buttress is also used to conduct rainwater from the "Cover (architecture)" roofs to the outside, these drains usually being decorated with grotesque figures, which are called gargoyles "Gárgoyle (architecture)").