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Fémnemfém, or metalloid, is a term used in chemistry to describe elements with intermediate properties between metals and nonmetals. There is no universal agreement on the exact list, but the most commonly cited metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium; some classifications also include polonium and astatine. The term reflects qualitative similarities rather than a rigid category.

Metalloids typically exhibit a mix of metallic and nonmetallic characteristics. They are often brittle solids with a metallic luster when polished, and many are semiconductors whose electrical conductivity can be controlled by doping, temperature, or pressure. Chemically, they tend to form covalent bonds and can display multiple oxidation states; several oxides are amphoteric, reacting with both acids and bases.

Role and uses: Silicon and germanium are the most important metalloids in modern electronics, serving as the basis for semiconductors and integrated circuits. Boron is used in glass and alloys; tellurium in thermoelectric devices; arsenic and antimony in specialty alloys and catalysts. Some metalloids also occur naturally with unique properties, such as borderline conductivity and reactivity.

Taxonomy: The metalloid label is a cross-cutting category rather than a strict chemical class. Its composition depends on chosen criteria and context; some periodic tables place metalloids on a diagonal line between metals and nonmetals, while others emphasize electronic structure or bonding behavior. As a result, the group is inherently loosely defined.