deoxyribonucleic acid, desoxyribonucleic acid, DNA(noun) (biochemistry) a long linear polymer found in the nucleus of a cell and formed from nucleotides and shaped like a double helix; associated with the transmission of genetic information.
But even adults don't often know what a notochord is. A notochord is a primitive beginning to the backbone. It appears in embryos as a small flexible rod made from cells from the mesoderm, which is one of the three layers of cells of embryos. Notochords are only found in the phylum chordata, a group of animals that includes humans.
This phylum includes all animals which have a hollow nerve cord and  a notochord at some stage during their development. In the case of  vertebrates, the notochord is present in the embryo, and develops  into the vertebral body. In the tunicates, the adult form no longer  has the notochord.