In Spain. Portugal and in some countries South America frequently used name or synonym for many different white grape varieties. The confusion is exacerbated by different spellings ("o" and "u"). Especially with the varieties grown in Portugal and Spain, there is often a lack of clarity as to what exactly is meant. The Portuguese DOC or Spanish DO regulations and grape catalogs are also of no help if only "Torrontés" is given there.
Source: Wine Grapes / J. Robinson, J. Harding, J. Vouillamoz / Penguin Books Ltd. 2012