Definition of "NNR"

(UK) Initialism of national nature reserve.  examples

(text messaging) Abbreviation of no need to respond or need not respond.  examples

(text messaging, uncommon) Initialism of no, not really.  examples

(UK, parenting, rare) Initialism of not nappy related (used in forums dedicated to nappies (diapers) to signify that the succeeding post is not related to nappies; i.e. it is off-topic).