A KN95 mask is a personal protective equipment (PPE) that protects the person wearing it from particles in the air. The KN95 mask follows the Chinese GB2626-2006 standard, which is different from the EU’s EN 149:2001+A1:2009 standard and the US NIOSH NIOSH-42C FR84 standard. A good overview can be found here.
There are many counterfeit or erroneous declarations on KN95 masks, so we recommend checking this before you buy, leading to sub-standard products. Opting for an FFP2 mask or N95 model might be a better choice.