What describes the wider spot when there are two follow spots focused on the same performer?

The term that best describes the wider spot created when two follow spots are focused on the same performer is "Overlay." When two spotlights overlap their beams on a performer, the resultant beam of light is broader and more diffuse than the individual beams. This technique can be used to enhance visibility and create a more pronounced effect on stage, often adding to the dramatic emphasis on an actor or a particular moment in a performance.

The other terms do not accurately describe this phenomenon: "Moon box" usually refers to a type of lighting effect or a particular fixture that mimics moonlight; "Limelight" historically refers to a method of stage lighting but does not pertain to the concept of overlapping beams; and "Luminaire" is a more general term for a complete light source, including its fixture, which does not convey the specific action or effect of two focused lights combining their output.