In facsimile, a frequency modulationsystem where one frequency represents picture black and another frequency represents picture white[?]. Frequencies between these two limits may represent shades of gray
An intentional frequency change used for modulation purposes
... and the vaginal opening.
In the human male, the urethra is about 8 inches (200 mm) long and opens at the end of the penis.
Medical problems of the urethra:
...