ClipArt ETC
In architecture, an opening or a panel dividing by cusps or foliations into four leaves, or more correctly the leaf-shaped figure formed by the cusps. It is an ornament which has been supposed to represents the four leaves of a cruciform flower, and is common in the tracery of Gothic windows.

Quatrefoil Architecture

In architecture, an opening or a panel dividing by cusps or foliations into four leaves, or more correctly…