The C++ serialization library cereal uses the acronym NVP several times in its documentation without mentioning what it means.
A quick web search brings up further hits related to boost serialization, and on first glance I couldn't spot a full spelling of the acronym either. It seems to be some kind of C++ serialization related slang.
What does it stand for?
It means "Name Value Pair".
KVP (Key-Value Pair) is another common acronym for the same concept you may have run into. They are interchangeable.
It seems to be some kind of C++ serialization related slang.
Not really. It's an acronym specific to boost::serialization. As far as I can tell, cereal inherited it out of its explicit positioning as an alternative to that original library.