Latim maxim meaning “no one gives what they do not have”. Sometimes referred to as the “nemo dat” rule or principle.
It refers to the question whether someone purporting to give or sell property has legal title or right to do so. If not, the gift or transfer will not take effect and cannot be enforced. The transferor’s title may be questionable because the property has been stolen or looted or acquired by fraud, or simply because of some error in the process of a prior sale or transfer.
By way of example (highlighted in bold): Skelwith (Leisure) Ltd v Armstrong  EWHC 2830 (Ch);  Ch 345 per Newey J:
“ The Court of Appeal decision in Mortgage Business plc v O’Shaughnessy  1 WLR 1521 indicates that the extent of the ‘owner’s powers’ of a ‘person entitled to be registered as the proprietor’ of an estate or charge (within section 24(b) of the Land Registration Act 2002) depends on whether the person in question has acquired ownership at law of the estate or charge. If he has not done so, the principle that ‘[a] person cannot grant a greater interest than he or she possesses’ (ie the principle expressed in the old maxim ‘nemo dat quod non habet‘) will apply in the absence of statutory provision otherwise. Although the Court of Appeal did not spell matters out in quite this way, it presumably took the view that the kinds of disposition ‘permitted by the general law’ for the purposes of section 23(1)(a) and section 23(2)(a) of the LRA 2002 were limited in the case of an equitable owner by the ‘nemo dat‘ principle.”