filtre

Filtre is the French noun for "filter." In general use, a filtre is a device, medium, or process that removes undesired components from a mixture or stream, or that restricts the content of information that passes through a system. The term is used across science, engineering, and everyday life to describe both physical barriers and abstract selection processes. Etymology traces to Old French filtre, from Latin filtrum, meaning filter.

Physical filtration covers devices and media that separate solids from liquids or gases. Examples include water and air filters, coffee and tea filters, and sediment filters in wastewater treatment. Filtration relies on interception, adsorption, or pressure-driven flow through porous materials, membranes, or activated carbon, capturing particles while allowing fluid to pass.

Electronic and signal processing use filters to shape frequency content. Analog filters implemented with resistors, capacitors, and inductors, or digital filters implemented by algorithms, remove unwanted frequency components or extract signals of interest. Common types include low-pass, high-pass, band-pass, and notch filters; design goals include attenuation characteristics, phase response, and stability.

Image and data filtering apply spatial or temporal kernels to smooth, sharpen, or detect features. Convolution with kernels such as Gaussian or Sobel operators reduces noise or enhances edges. In data management, filters may restrict or transform streams of records, e.g., query filters or content filters in information systems.

While "filtre" is a French term, similar concepts exist under many names in different languages. In French-language contexts, the word is used in science, consumer products, and technology to name devices and methods that separate, suppress, or refine content or materials.