An antiviral is a type of drug specifically designed to treat viral infections. Unlike antibiotics, which treat infections caused by bacteria, antivirals work against specific viruses by interfering with their ability to replicate or function. Antivirals can reduce symptoms and shorten the amount of time you are sick, reduce the risk of developing severe illness, and can also lower your risk of getting or spreading certain viruses. 

Source:  What Is an Antiviral?, National Foundation for Infectious Diseases  (NFID)