Original: Wade–Giles' was the main system of transcription in the English-speaking world for most of the 20th century, used in several standard reference books and in all books about China published before 1979.
Simplified: Wade-Giles was the main system of transliteration in the English-speaking world for much of the 20th century. It is used in several standard reference books. It is also used in all books about China published before 1979.