The GOC has recently introduced a new term biological phase (GO:0044848), as a direct subclass of biological process. This class represents a distinct period or stage during which biological processes can occur. Biological phases do not share any is_a parent terms with other biological processes (i.e. they are is_a disjoint). They can be related to other biological processes with happens_during relationships e.g. DNA replication happens_during S-phase. They can also be regulated by other biological processes. Examples of biological phases are cell cycle phases such as metaphase and prophase and developmental phases such as menarche and estrus.