A metalloid is a type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. There is no standard definition of a metalloid and no complete agreement on which elements are metalloids. Despite the lack of specificity, the term remains in use in the literature of chemistry. Metalloids typically have a metallic appearance but are brittle and not as malleable as metals.

वे तत्व जिनमें धातु तथा अधातु के गुण पाये जाते हैं उन्हें उपधातु कहते हैं जैसे कार्बन, बोरान आदि।