What is it?
Definitions: “A genome is an organism’s complete set of DNA, including all of its genes. Each genome contains all of the information needed to build and maintain that organism.” (from http://ghr.nlm.nih.gov/handbook/hgp/genome). The same source defines a gene as “the basic physical and functional unit of heredity”, and notes that genes are segments of DNA molecules that act as instructions for products (proteins or RNA molecules) that function in growth and development of cells and organisms.
Genomics is “the branch of molecular biology concerned with the structure, function, evolution, and mapping of genomes” (Google definition).