The focus (or foci - plural) of a conic section is the point (or points) from which the distance to each point on the graph of the conic section is constant as defined by the specific conic section's equation.

The focus (or foci - plural) of a conic section is the point (or points) from which the distance to each point on the graph of the conic section is constant as defined by the specific conic section's equation.