The state of being incapable of prescription, because - first and formost it is uncountable or considered to be uncountable.
A property which is held in trust is imprescriptible; that is the trustee cannot acquire a title to it by prescription; nor can the borrower of a thing get a right to it by any lapse of time. html 
The notion is closely linked to inappropriability
Yan Thomas writes about the character of public and sacred "things" in legal texts that are more than 2000 years old:
Toute estimation eût abouti à leur rachat, contrairement au principe de l'imprescriptibilité de leur statut de choses inappropriables. ... l, la chose échappait à toute mesure de sa valeur.
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# See also
# Sources
Yan Thomas (2002): La Valeur des Choses, pdf