Genomic DNA is the name for the DNA forming the (nuclear) genome of the relevant organism. The marking helps to distinguish between nuclear - genomic DNA and extranuclear DNA contained in mitochondria (mtDNA) or in plastids.
Dictionary.com. gDNA definition at Dictionary.com [online]. ©2010. [cit. 17-03-2023]. <https://www.dictionary.com/browse/gdna>.