What’s the difference between ‘cemetery’ and ‘graveyard’?

Make no bones about it—no one is going to ghost you for making a faux pas by mixing up graveyard and cemetery because the two words are synonyms; they both refer to a place where dead bodies are buried.

Graveyard often implies that the burial ground in question—such as one that might be next to a church or homestead—is small, but no one should have a bone to pick with you if you use it interchangeably with cemetery. There are no size requirements for graveyards or cemeteries beyond what zoning laws dictate.

Over a millennium ago, an ancient society of hunter-gatherers in Argentina’s Patagonia region buried one of its members in a small cemetery.
—Sonja Anderson, Smithsonian Magazine, 15 Apr. 2024

… Tainiaro, an area in Finland that could be home to one of the largest Stone Age cemeteries in Europe, except for the fact no remains have ever been found in the hundreds of burial plots. It is a mystery that has left archaeologists baffled for decades. … Now, a team led by archaeologist Dr Aki Hakonen from the University of Oulu in Finland, argues that Tainiaro was once a huge graveyard – and they think they know where the bodies went.
— Katherine Fidler, The Metro (London, United Kingdom), 5 Dec. 2023

Graveyard is also sometimes used figuratively for places where things are left, thrown away, or otherwise resemble human cemeteries in some way:

The atmosphere, too, has changed. Children still entertain themselves, devising games in the tree graveyards that ring parts of the island, but the electric energy of a busy fishing village has given way to a sense of lethargy.
— Tommy Trenchard, Hakai Magazine, 19 Mar. 2024

Cemetery is the older of the two words in English, first used in the 1400s and descended ultimately from the Greek word koimētērion, meaning “sleeping chamber” or “burial place.” The first-known use of graveyard in print occurred a few centuries later, in the mid-1700s.