Introns are sections of noncoding DNA that separate exons within a gene locus. However, between different gene loci, I also would assume there to be noncoding regions of DNA. What are these regions called? (And if my assumption is wrong, then please correct me.)
These regions, if unannotated, are simply called intergenic regions.
Sometimes, if a large section of chromatin is regulated by an enhancer/silencer/locus control element, then there are boundary elements that demarcate this chromatin region and prevent the spread of the chromatin state to neighbouring regions.
It would be valid to call them "intergenic regions", but this is just another way of saying that they are the regions between genes. I don't think you can do much more because they are not homogenous in nature. Some may be short and perhaps lack any other function than that described by @WYSIWYG, others may be very long and have enhancers and regulatory elements for proximal or distal genes, simple repeated sequences, pseudogenes, replication origins etc. etc.