What shape is the defining arch of Gothic architecture?

The defining arch of Gothic architecture is the pointed arch.

Also called an ogival or Gothic arch, it has two curved sides that meet at a pointed crown. Medieval builders used it in arcades, doorways, windows, and vaulting, making it the most recognizable structural feature of the Gothic style.

The pointed form helped builders control the distribution of weight and thrust more flexibly than a semicircular Romanesque arch. Combined with rib vaults and flying buttresses, it allowed churches to rise higher and use thinner walls with much larger stained-glass windows.

The arch itself was not invented by Gothic architects. Pointed arches had appeared earlier in Byzantine, Sasanian, and Islamic architecture, among other traditions. Gothic builders adopted and systematized the form in western Europe, especially from the 12th century onward. Ogee, horseshoe, and round arches are different arch types.