Period instruments
During the 20th century musicians started to realize that the way we play the music of Bach and other composers was making the music sound different from how it would have been first heard.  People became interested in hearing what the music would have sounded like back in the 17th and early 18th centuries (the Baroque period). Few of the old instruments still existed and many that had survived had been “modernized”.  So instrument makers started to make instruments in the old ways.  Some musicians and orchestras started to play these instruments.  The instruments are often called “period instruments” (or "authentic instruments" or "historical instruments") because they are made so that they are like instruments of earlier periods.