What does SSD mean in Singapore real estate

Seller’s Stamp Duty (SSD) is a tax payable by property owners who sell their residential or industrial properties within certain holding periods. The rate and holding period are determined by the date of purchase. For residential properties purchased on or after 11 March 2017, SSD may apply if sold within three or four years. For industrial properties purchased on or after 12 January 2013, SSD applies if sold within three years. After these holding periods, no SSD is payable.