The G0 phase is a stage in the cell cycle where cells exit from active division and enter a resting state. During this phase, cells are metabolically active but do not prepare to divide. This can occur in response to various signals, allowing cells to conserve energy and resources when conditions are not favorable for growth. Cells in the G0 phase can remain in this state for extended periods, sometimes even years. Some cells, like neurons and muscle cells, typically remain in G0 permanently, while others can re-enter the cell cycle when conditions improve, transitioning back to the G1 phase to begin dividing again.