NNR

(Internet) Abbreviation of no need to respond or need not respond.

(Internet) Initialism of no, not really.

(UK, 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).

(UK) Initialism of national nature reserve.