Set In Jello Edit Meaning

1.

A description of a document (for instance, a programming schedule for a convention) that, while written or printed, is still at the given moment highly flexible and can be reshaped with little to no effort.

Derived by analogue to set in stone, and with lack of a better substance to set soemthing in that would require flexibility.

The payment terms for this contract are still set in jello.