Answer:
A glide reflection is a two-step procedure in which the translation normally occurs along the line of reflection after the reflection.
What's the difference between reflection and glide reflection?
A reflection is a single action, such as the reflection across y = x in the blue pre-image and the black dotted-line picture below.
A glide reflection is a two-step procedure in which the translation normally occurs along the line of reflection after the reflection.
In such situation, the blue pre-image is reflected across y = x and then translated by a factor of two to form the green picture.
The figure appears to be moving along the line after several repetitions.
A sine wave resembles the sine from zero to pi that has been repeatedly translated from "pi, 0" across the x-axis.
See the attachment. (Pre-image in blue Dots indicate reflection. Glider reflection picture is green.)
Cheers,
ROR