A histone is a protein that provides structural support for a chromosome. Each chromosome contains a long molecule of DNA, which must fit into the cell nucleus. To do that, the DNA wraps around complexes of histone proteins, giving the chromosome a more compact shape. Histones also play a role in the regulation of gene expression.
Histones are proteins that are critical in the packing of DNA into the cell and into chromatin and chromosomes. They're also very important for regulation of genes. We used to think that histones acted essentially as DNA suitcases to sort of hold the DNA, but it was very clear that histones are regulated and have a lot to do with when genes are turned on and turned off. You can think about them as a regulated suitcase that determines when the suitcase is opened and a gene gets out. So they turn out to have very important functions, not only structurally, but also in the regulation of gene function in expression.