The Key lime (Citrus ×aurantiifolia) is a citrus hybrid (C. micrantha x C. medica) with a globose fruit, 2.5–5 cm in diameter (1–2 in), that is yellow when ripe but usually picked green commercially.
It is smaller and seedier, with a higher acidity, a stronger aroma, and a thinner rind, than that of the Persian lime (Citrus × latifolia). It is valued for its unique flavor compared to other limes, with the Key lime usually having a more sweet and bitter flavor. The name comes from its association with the Florida Keys, where it is best known as the flavoring ingredient in Key lime pie. It is also known as West Indian lime, bartender’s lime, Omani lime, or Mexican lime, the last classified as a distinct race with a thicker skin and darker green color. Philippine varieties have various names, including dayap and bilolo.