the genome
If a gene is a single recipe, the genome is the entire cookbook: the complete set of DNA in an organism, every gene plus all the DNA in between. For a human that means roughly three billion base pairs of DNA, copied into almost every cell of the body. The genome is the master archive from which a cell pulls whatever instructions it needs, when it needs them.
It helps to picture the layout. The human genome is split across 23 pairs of chromosomes in the nucleus, plus a tiny separate genome inside the mitochondria. Strikingly, only a small fraction of it, on the order of one to two percent, directly codes for proteins; the rest is non-coding DNA that includes regulatory switches, genes for RNA that never becomes protein, repeated sequences, and the relics of ancient viruses. Calling all of that 'junk' was a premature label, because much of it does real work in controlling when and where genes are read.
The genome concept reorganized biology by inviting us to study an organism's instructions as one whole, finite, readable object rather than gene by gene. That shift made the Human Genome Project conceivable and gave rise to genomics: comparing whole genomes across people and species, finding the variants linked to disease, and mapping the regulatory landscape. The genome is the territory; individual genes are landmarks on it.
Every cell in your body carries the same ~3 billion-base-pair genome, yet a neuron and a white blood cell look and act nothing alike — because each reads out a different subset of that one shared archive.
One genome, many cell types — differences come from what is read, not what is stored.
Genome size does not track an organism's complexity (the C-value paradox): some amoebas and plants have genomes far larger than ours. And most of the human genome is non-coding, not 'junk' — much of it regulates the rest.