Hi Alvin, thanks for writing to us on AskGuru.
The term sub-sale refers to a property that's bought by a buyer and then sold to another buyer before the unit is completed. Sales of such residential properties are governed by the Housing Developers (Control and Licensing Act).
Here’s what you need to know about sub-sale properties: https://www.propertyguru.com.sg/property-guides/quick-guide-to-everything-you-need-to-know-about-sub-sale-27932
Hope this answers your question.