Answer
What does it mean when crowdfunding money is held in escrow?
Short answer
It means the money sits with a neutral third party until an agreed condition is met, rather than going straight to the person raising it. On CoFunders that third party is a program on a public network, not a company.
Escrow is an old idea and it exists because of one problem: two parties want to trade, and whoever moves first is exposed. A backer who pays up front is trusting a founder who has not built anything yet; a founder who builds first is trusting backers who have not paid. Escrow removes the choice of who goes first by having neither side hold the money.
In crowdfunding the agreed condition is the funding goal. Pledges accumulate in the escrow, and the money is released to the founder only if the target is reached by the deadline. Miss it, and the same escrow returns everything.
The difference between platforms is what the escrow actually is. Usually it is a bank account belonging to the platform, governed by its terms of service, and you are trusting a company to follow its own policy. Here it is a program account on Solana: the address is public, the balance is public, and the rules that move the money are code that was published before your pledge went in and cannot be edited afterwards to suit anybody.
That last part is the whole argument. A policy can change and a company can fail. The condition releasing a campaign's escrow was fixed when the campaign opened, and it applies identically to a campaign we like and one we do not.