Complex sentence: During the 1920s and 30s all unipolar (single terminal) high voltage medical coils came to be called Oudin coils, so today's unipolar Tesla coils are sometimes referred to as "Oudin coils".
Split into simpler sentences: During the 1920s and 30s terminology changed, and all unipolar (single terminal) high voltage medical coils came to be called Oudin coils. Therefore today unipolar Tesla coils are sometimes referred to as "Oudin coils".