The 16th century Huguenots were French Protestants (puritans) who held to the Reformed, or Calvinist, tradition of Protestantism.
The origin of the word itself is unknown.
According to Roche 'The Days of the Upright, A History of the Huguenots' (1965) the word is :
[…] a combination of a Dutch and a German word. In the Dutch-speaking North of France, Bible students who gathered in each other's houses to study secretly were called Huis Genooten ("housemates") while on the Swiss and German borders they were termed Eid Genossen, or "oath fellows", that is, persons bound to each other by an oath. Gallicised into "Huguenot", often used deprecatingly, the word became, during two and a half centuries of terror and triumph, a badge of enduring honour and courage."
However, according to Etymology Online there have been at least seven different serious proposals as to the word's origin. Pointing out that Brachet's French etymology dictionary says, "No word has had more said and written about it"