The act or process of introducing something additional or extraneous between other parts.
Something interpolated, as a passage introduced into a text.
Mathematics. A. The process of determining the value of a function between two points at which it has prescribed values. B. A similar process using more than two points at which the function has prescribed values. C. The process of approximating a given function by using its values at a discrete set of points.
When men interpolate, it is because they believe their interpolation seriously needed.
-- Thomas Paine, The Age of Reason
"I am inclined to think," he added after a moment, once he had their attention again, "that if some pages were interpolated it was either done around the time of the original edition, or now, in our time.
-- Arturo Pérez-Reverte, The Dumas Club
Interpolation is derived from the Latin word interpolātus, meaning “to refurbish or touch up.”