The word 滤光镜 is formed through the direct combination of three meaningful characters: 滤, which means "to filter"; 光, meaning "light"; and 镜, meaning "mirror" or "lens". Together, they create a compound term where 滤 modifies 光 to specify the action of filtering light, and 镜 denotes the physical instrument, resulting in a word that literally means "light-filtering lens" and refers to an optical filter.