ENS domain is a way to identify an Ethereum address by labelling it, via a service provided by ENS.domains. This is similar to how an unique url points to a unique webserver.
By using the juicebox.eth ENS, we would identify the address of the multisig as the official one. Juicebox has already registered juicebox.eth and this proposal is to fund the registry extension of the domain for the 10 coming years.