A royalty is a share of the money a book earns. Check what the share is based on. Some contracts pay on the list price, others on net receipts, which is what the publisher actually receives after discounts. A percentage of net can be much lower than the same percentage of list. Ask for the definition in writing. Also ask how returns, discounts and special sales affect the rate, since these can change what lands in your account.
Traditional publishing may include an advance, which is a payment against future royalties. You usually keep the advance even if the book does not earn it back, but you will not receive more until sales cover it. Royalties are generally paid on a schedule, often twice a year, with a statement. Retail platforms for self-publishers typically pay monthly, with a delay, and set a minimum threshold.
When reading a contract, look for the rights granted, the term, the territory, the royalty rates for each format, the reversion clause that returns rights if the book goes out of print, any option on your next book, and who controls the cover and the edits. Walk away from deals that demand fees for a service labelled as traditional publishing. A literary agent, publishing attorney or an author organization such as the Authors Guild can help you review terms. Never feel pressured to sign quickly.
Be careful with a few common clauses. A non-compete clause can limit what else you publish. A right of first refusal or option lets the publisher see your next book first. Terms for returns and reserves against returns can delay your payments. Subsidiary rights, such as audio, translation and film, may be split between you and the publisher, so check the percentages. Keep copies of every royalty statement, and if something looks wrong, ask politely for an explanation or request an audit if your contract allows it.
At Small Press Distribution, authors keep copyright, credit and royalties, and we never take royalties. A fixed quote is agreed in writing before work begins and split into milestones, with no hidden fees.