What is the G0 part of the cell cycle?

The G0 part of the cell cycle is the phase during which a cell is neither dividing nor preparing to divide. Cells exist in a quiescent state after they exit the cell cycle. In the G0 phase, a cell is carrying out its basic cellular functions. G0 may be a permanent state for some cells, while other cells may restart division if they receive the external cues to do so. Mature cardiac muscle and nerve cells, which never or rarely divide remain in the G0 phase permanently. The G0 phase can also be thought of as an extension of the interphase; this due to the fact that cells can enter from the G1 phase of interphase.