In molecular biology, "junk"
DNA is a collective label for the portions of the DNA sequence of a
chromosome or a genome for which no function has yet been identified.
About 98.5% of the human genome has been designated as "junk", including
most sequences within introns and most intergenic DNA. While much of this
sequence is probably an evolutionary artifact that serves no present-day
purpose, some may function in ways that are not currently understood. ...
Junk DNA , Wikipedia, The Free Encyclopedia