Instead, there are two focal points, called the foci, as you will see presently.

The villages of New England—the foci of blue laws and Puritanism.

The earth's orbit is an ellipse, one of the foci of which is occupied by the sun.

Each one is called a focus, and an ellipse can only have one pair of foci.

It has two foci, S and S', fixed points, by the aid of which we may trace the curve.

They were called "foci" and "factors," and all manner of imposing names.

Religion has two foci to determine,—the divine nature and the human.

At one of the points mentioned, which are the foci, let us fasten an orange.

They are, in fact, ellipsesone of the foci being the point about which the revolution is made.

If c is negative, √c becomes imaginary, and there are no foci.