Zinc finger nucleases (or ZFN) was a tool used to target genes and change DNA. It was one of three methods of changing the genome with engineered nucleases. It is now superseded.
Zinc fingers are man-made molecules made of a protein and zinc. Each binds to a specific DNA. Zinc-finger nucleases (ZFNs) are enzymes got by fusing a zinc finger to a DNA cleavage enzyme called a Fokl. So the ZFN binds onto a specific DNA sequence, then snips it in two places. Regular cell enzymes stick the ends together, minus the bit snipped out (DNA repair).
Each ZFN is made to use on a single gene which is called a “target gene” or “target DNA”. They can be designed to work on specific parts of genes to create a desired change. The two types of DNA changes are mutations such as deletions and insertions. Genetics research looks at the mutated subjects (animals, plants, bacteria) to find out what the particular gene does.