1. A situation or surrounding substance within which something else originates, develops, or is contained: "Freedom of expression is the matrix, the indispensable condition, of nearly every form of freedom" (Benjamin N. Cardozo).

2. The womb.

3. Anatomy. a. The formative cells or tissue of a fingernail, toenail, or tooth. b. See ground substance.

4. Geology. a. The solid matter in which a fossil or crystal is embedded. b. Groundmass.

5. A mold or die.

6. The principal metal in an alloy, as the iron in steel.

7. A binding substance, as cement in concrete.

8. a. Mathematics. A rectangular array of numeric or algebraic quantities subject to mathematical operations. b. Something resembling such an array, as in the regular formation of elements into columns and rows.

9. Computer Science. The network of intersections between input and output leads in a computer, functioning as an encoder or a decoder.

10. Printing. a. A mold used in stereotyping and designed to receive positive impressions of type or illustrations from which metal plates can be cast. Also called mat2. b. A metal plate used for casting typefaces.

11. An electroplated impression of a phonograph record used to make duplicate records.