Genomes are all the DNA in an organism, needed to create and support its self.
In diploid organisms, it is the information in the base sequence of DNA included in one set of chromosome. In humans, there exists one X or Y sex chromosome, so a human genome is the information included in 22 sets of autosomes plus an X and Y sex chromosome, making it 24 chromosomes total.
Genetic information is the nitrogenous bases' sequence of the DNA, and the number of base pairs of the genomic DNA is called its genome size.
It is not always that a more complex organism has a bigger genome size, and for instance, some amphibians have 30 times the size of human genomes. This is because there are parts of genomes that are unused. In humans, the 100 thousand genes only contribute to 5 to 10 percent of the whole human genome. The left 90 to 95 percent is thought to be unused, and are called junk DNA.