Herpes zoster, colloquially known as shingles, is the reactivation of varicella zoster virus, or VZV. The virus, one of the Herpesviridae group, leads to a group of painful blisters over the area of a dermatome.
After an attack of chicken pox, the varicella-zoster virus retreats to nerve cells within the ganglion or the spinal cord, where it will lie dormant for several months up to several decades. Aging, stress, or disease will cause the varicella zoster virus to reactivate and reproduce, at which point it is known as herpes zoster. Once activated, the herpes zoster virus travels along the path of a nerve to the skin's surface, where it causes shingles. 
Treatment is generally with antiviral drugs such as acyclovir (Zovirax), or prodrugs such as famciclovir (Famvir), or valacyclovir (Valtrex). Maximum efficacy of antiviral drugs occurs if the treatment is commenced with 72 hours of appearance of definitive symptoms.