A syndicate allows investors to participate in a lead investor's deals. In exchange, investors pay the lead carry. Here's an example:
Sara, a notable angel investor, decides to lead a syndicate. The syndicate investors agree to invest $200K total in each of her future deals and pay her 15% carry.
When Sara makes her next investment, she offers to invest $250K in the company. She personally invests $50K and offers the remaining $200K to her syndicate.
If the investment is successful, the syndicate investors first receive their $200K, after which every dollar of the syndicate’s profit is split 80% to the syndicate investors, 15% to Sara and 5% to AngelList.