According to the Centre for Disease Control (CDC), the “N” stands for “Not resistant to oil”. The 'N95' designation means that when subjected to careful testing, the respirator blocks at least 95 per cent of very small (0.3 microns) test particles.
An N95 respirator is a respiratory protective device designed to achieve a very close facial fit and very efficient filtration of airborne particles. Note that the edges of the respirator are designed to form a seal around the nose and mouth. Surgical N95 Respirators are commonly used in healthcare settings and are a subset of N95 Filtering Facepiece Respirators (FFRs), often referred to as N95s.