Here's the definition the Frankfurt/Rhein-Main campaign group for UBI is working with:
Unconditional Basic Income is an income that meets the following twelve criteria:
1. It is universal, everybody is entitled to it without means testing.
2. It is individual, no matter how old, whether married or not, living in a household with others or not.
3. It is high enough to secure existence and basic societal participation; it provides for a modest life in dignity.
4. It is unconditional, i.e. it is granted without any work requirement or willingness to work; it is not a wage.
5. It is paid at regular intervals, for instance monthly, not a one-off grant.
6. It is paid in a legal tender, neither in vouchers or in-kind, nor in the fiat money of the commercial banks. We strongly support the introduction of a Central Bank Digital Currency (CBDC) without the abolition of hard cash.
7. Its amount (as well as its introduction) is decided upon in periodic referenda.
8. The amount is the same for everybody, there's no discrimination for age or place of residence.
9. It is accompanied by social contributions that cover individual additional demands, f.x. in case of disability, transitorily also in case of increased housing costs.
10. In the midterm it will be introduced world-wide, in the near term on the highest level at which the administrative requirements for it are met (i.e. nationally or e.g. in the European Union).
11. It is accompanied by an adequate regulatory and tax policy framework that ensures that the generation of social prosperity does not destroy the balance of ecosystems and thus does not occur at the expense of the life chances of future generations.
12. It is financed in a way to reduce wealth inequality.