Viral life cycle
Some viruses can "hide" inside another cell, either to defend itself against the host cell defenses or immune system, or because it is not in the best interest of the virus to make more copies at the time.  This hiding is called latency. During this time, the virus will not produce any copies, it will remain inactive until external stimuli (such as light or stress) prompts it into activation, or the restart of the life cycle.