Histone modification refers to the chemical changes that occur on the proteins called histones, which help package and organize DNA in the cell nucleus. These modifications can include the addition or removal of various chemical groups, such as methyl or acetyl groups. By altering the structure of histones, these modifications can influence how tightly or loosely DNA is wrapped around them, affecting gene expression. These changes play a crucial role in regulating cellular processes, including gene activation and silencing. Different patterns of histone modifications can lead to distinct outcomes in cell function and identity, making them essential for processes like development, differentiation, and response to environmental signals.