What is a 6 year shield annuity?

A 6-year shield annuity refers to a tax strategy under the 1997 Income Tax Assessment Act (ITAA 1997), where a residential property that has been rented out for cumulative periods up to 6 years can be sold without capital gains tax (CGT), as long as it was the owner's main residence at some point and certain conditions are met regarding the timing of the rental periods and the property's use as a primary home.