What does SYN mean in the slimming world?

Excuse me, could you clarify for me what the term 'SYN' stands for in the context of the slimming world? I've come across it a few times but haven't been able to find a definitive explanation. Is it a specific diet plan, a type of supplement, or perhaps a term related to weight loss strategies? I'd appreciate any insights you could provide to help me understand this term better.