Why do people call DNA the genetic code and how does it work?

Genetic code is the term we use for the way that the four bases of DNA--the A, C, G, and Ts--are strung together in a way that the cellular machinery, the ribosome, can read them and turn them into a protein. In the genetic code, each three nucleotides in a row count as a triplet and code for a single amino acid. Genetic code. The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells ... Those genes that code for proteins are composed of tri-nucleotide units called codons, each coding for a single amino acid. DNA contains the instructions needed for an organism to develop, survive and reproduce. To carry out these functions, DNA sequences must be converted into messages that can be used to produce proteins, which are the complex molecules that do most of the work in our bodies.

The genetic code is (nearly) universal

Even in organisms that don't use the "standard" code, the differences are relatively small, such as a change in the amino acid encoded by a particular codon. A genetic code shared by diverse organisms provides important evidence for the common origin of life on Earth.