The Terraform auction took place in December 2017 and was the first time investors could buy LAND within Genesis City, the first city in Decentraland. The Terraform auction took the form of an auction style bidding process where investors would bid on plots of LAND just as you would do AFK.
Over 3000 unique addresses took part in the auction, and over 70,000 LAND parcels sold (from 90,000 in total). All MANA used to purchase LAND parcels was burned. This totalled 160,000,000+ MANA.
You can read more about the Terraform auction here