A syndicate lets a group of lottery players buy shares in the same numbers. This means they pay less for each chance to win, so for the normal price of a single ticket they might get shares in 50 tickets (for example). Of course, if they share the cost of the ticket then they share the prize money too, but millions of players think it’s worth sharing to get more chances of winning.
For example, let’s say that 10 people play the US Powerball as a syndicate. Their syndicate buys 1 ticket for the next draw. It wins the jackpot! - $10 Million, so each member receives $1 million (10 percent) of the jackpot prize. And if a player bought 2 shares, they would receive $2 million, 3 shares would pay them $3 million, etc.