One year of inactivity, actually. Two years is the expiration period for certain warnings. :)

No, I think you're confusing the frozen message (which displays immediately and indicates that names clear a year from the date of freezing), the upcoming clearing message (which displays after a period of inactivity but before the year is up, and alerts to the date that it hits one year and names will become available), and the inactivity message (which displays on accounts inactive for one year and indicates that names may be used).