Vertical Reflection Definition
A vertical reflection is a reflection in which a plane figure flips over vertically. A vertical reflection has a horizontal axis of reflection. In the case of a vertical reflection given a function of a graph f(x) outputs are changed and the function becomes -f(x). This means y-coordinates are reversed from positive to negative and negative to positive thus reflecting the graph vertically around the x-axis.
Sterling, Mary Jane, et al. “Reflecting Functions Vertically or Horizontally.” Dummies, www.dummies.com/education/math/trigonometry/reflecting-functions-vertically-or-horizontally/.