In the West, the term seiyuu has come to denote the Japanese voice actor while "voice actor" is used to indicate the English-speaking actor after a movie or series has been translated.
The word seiyuu is actually a shortened version of the kanji used for "voice actor" - koe no haiyu, however many older voice actors resent this particular term.
Originally, dubbing and voice-overs were done by stage and film actors who used only their own voice, while true seiyuus were used only for "character voices" and considered to be a "lesser" type of actor. But after the anime boom, the term seiyuu became widely known and was considered to be interchangeable with the term "voice actor", a fact that some older actors found insulting.
Yet, despite this once dismissive connotation, today's seiyuus enjoy a variety of work and are held in high regard among fans and industry professionals alike. And although many do still branch over into film and television (as well as music), such an adaptation is not required to build a thriving career or achieve widespread popularity.
In fact, seiyuus are so respected that Japan has several magazines devoted to the art of voice-acting and also boasts over one hundred seiyuu "schools" to help train and prepare aspiring voice actors.