Jim Kelley wrote:
"In what way is it (an electrostatic field) not (stationary)?"

Terman was refering to an electromagnetic (radio) wave. It is a
peculiarity of "old-speak" to call an electric field an electrostatic
field.

As Cecil reminds us, radio waves are always in motion. But, their
superposition may produce a stationary wave called a standing wave.

Best regards, Richard Harrison, KB5WZI