They're called lairs because it's an actual subtype they have.
Before they were errata'd to include the "lair" part above the text box, they'd say things like...
"Darigaaz's Caldera is a Lair in addition to its land type."
Since these are, for all intents and purposes, dual lands, I suspect that they'll simply be referred to as "the new dual lands" or "the Ravnica dual lands" or something. I mean, Onslaught introduced a new (and better) type of fetchland, and I've usually seen them referred to as "Onslaught fetchlands."