Confocal means having the same foci.

In conic sections, it is said of two ellipses, two hyperbolas, or an ellipse and a hyperbola which share both foci with each other. If an ellipse and a hyperbola are confocal, they are perpendicular to each other.

In optics, it means that one focus of one lens is the same as one focus of the next lens.

See also: confocal laser scanning microscopy.