A “Grant of Probate” comes from the Supreme Court and is the official acknowledgement that on the available evidence:
the deceased is in fact deceased
a will is the last will of the deceased
the executor is authorised to collect assets from persons holding them on behalf of the deceased.
Probate is granted by the Supreme Court (although you don't have to go to court unless there is a dispute about the will)
People paying assets of the deceased to the Executor named in the grant of probate are protected from future claims by other persons even if the probate is overturned by
Probate can be revoked if the will is proven to be not the last or other defects found in the process (ie. the person is not dead).
in that case the Executor may have to pay the money back to the estate (even if they have paid it out to other beneficiaries - the Executor would then have a right to take action to recover from such beneficiaries).