Definition - What does Filter mean?
A filter is a porous mechanical or chemical device used to remove solid particles, impurities and other undesired deposits present in a fluid. Filters are typically permeable, ranging widely in terms of applications depending on the size of particles to be separated. Among other uses, filters are used to purify liquids such as oil and gases such as air.
Corrosionpedia explains Filter
Most industrial filters are used to purify liquids and gaseous compounds. As such, it is vital that the materials used to produce the filter have a high rate of corrosion resistance to maintain optimal filter performance. Stainless steel should be used when possible, with supporting layers of epoxy or other coatings for added protection against corrosion. The lack of a proper corrosion preventative material may result in the complete disintegration of the filter or buildup of unwanted debris, which in turn could lead to crevice corrosion. This build-up is known as fouling.