It's important to specify the context of the quote. Your quote is from a young adult FANTASY novel by Rachel Hartman who lives in Canada right now: http://rachelhartmanbooks.com/about/ "Pyria," which is apparently an item in this fantasy world, is defined in the book itself: "The key to drachomania is setting the monster on fire. We've got pyria - St. Ogdo's fire - which clings to them and is not easily extinguished." Perhaps the author came up with the word "pyria" from the word "pyre," which generally refers to a funeral pile of firewood or something similar for burning a dead body.

Given the context that appears to be a person's name, though it is also the name of a gum disease.