Royalties & author's rights
Both the legal framework protecting the work and, by extension, the author's proportional remuneration on sales.
The expression covers two linked realities. Legally, author's rights (copyright) protect any original work from its creation, with no formality: in French law they include moral rights (attribution, integrity — perpetual and inalienable) and economic rights (reproduction, performance — licensable by contract, which is precisely what a publishing contract does). Economically, "royalties" name the author's proportional remuneration on sales.
Two practical consequences for the writer: no need to "register" a text to be protected (protection is born with creation, though proof of anteriority can help in a dispute); and a publishing contract is a rights license whose every line — scope, duration, territories, percentages per exploitation — should be read and negotiated.
Example
Moral right: your name on the work, forever. Economic rights: what the contract licenses, frames and pays.