The phrase "big fundraiser" refers to an event or activity organized to collect a large amount of money for a specific cause or charity. Full definition
You can do this at your shelter or in a more «romantic» location like a local animal friendly restaurant where you can turn this into an even bigger fundraiser! (charitypaws.com)
The Knight Pack Walk is the clubs biggest fundraiser of the year. (wbng.com)
He is also a leader on the March of Dimes national board of trustees and was named the 2015 national chair of the March for Babies — the nation's biggest fundraiser for mom and baby health. (cnbc.com)