When does holding or renting out property become a 'taxable business' in the UAE?

When the activity needs a commercial or trade licence. Passive, long-term letting of a property you own personally generally stays out of scope. But frequent buy-and-sell with a clear profit motive, property development, or a licensed leasing operation counts as a 'business.' Once that licensed activity's turnover exceeds AED 1 million in a calendar year, a natural person falls under 9% corporate tax. (verify with an adviser)