What is the "Fleetwood Mac sound" anyway?

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I'm referring to the Bob Welch and Rumours eras specifically. I've heard the term "Fleetwood Mac sound" bandied about a bit. Someone might be talking about one of Lindsey's Tusk songs, or For Your Love, and say that the song doesn't have that "Fleetwood Mac sound."

However, I've never been able to figure just what that "sound" is. If I were to play someone who'd never heard a Fleetwood Mac song instrumental versions of Tusk, Landslide, and Oh Daddy, would they recognize them as being from the same band? Oddly enough the closest I've come to identifying the Fleetwood Mac sound was Warren Zevon's Werewolves of London, but even then it was just because Mick and John played on it.