What is N95 mask?

Also known as the N95 respirator, the N95 mask is a lightweight, nose-and-mouth respirator that can provide some level of protection for the wearer from viruses, including avian flu. The N95 designation is an efficiency rating that means the mask blocks about 95 percent of particles that are 0.3 microns in size or larger. The Centers For Disease Control and Prevention (CDC) has recommended the use of N95 masks for protection against the avian flu virus.
Source http://www.fao.org/avianflu/en/glossary.html