I have been reading "The Dark Legacy of Shannara" series by Terry Brooks and a couple of characters possess the power of the Wishsong. It seems a rather powerful power to possess, but I am only provided examples of its capabilities in this series.
Is there a book or series he has written which explains the Wishsong in more detail? I don't wish to read all his books (at least not at this time) but I am quite interested in understanding more about this magic.
The Wishsong of Shannara, book three in the original Shannara series, explains the Wishsong in as much detail as can be found.
There is an extensive description of the working (and theory) behind the Wishsong in the book "Wishsong of Shannara".
You can also find out more by visiting the Shannara Wikia which provides a reasonable overview without too many spoilers;
The Wishsong is a magic that is controlled by singing. Brin Ohmsford could use it to dramatically change nature, in her childhood, she changed the leaves of a tree from Green to Brown in the summer, or it could be used as a weapon. Jair Ohmsford could only use it to create illusions. Par Ohmsford at first could only use the wishsong to create images but it evolved into an extremely powerful weapon, which he ultimately used to destroy Rimmer Dall and all of the Shadowen. Other Ohmsford family members have the power of the Wishsong as well, either in the form to create illusions or as a powerful weapon.
Additionally, the book Ilse Witch also contains some info about how Wishsingers learn how to control their powers.
It should be noted that like most magic in fantasy, the actual powers shown seem to vary greatly between books and tend obey the trope "New Powers as the Plot Demands"
The wishsong was actually started in the elfstones. Too much use of the elfstones to protect the choosen Emberle?(sp?) changed the father this wasn't noticed until the next generation. After that it passed to the two children and then there was some variation in every generation afterward.
