A matrix is a rectangular array of numbers, symbols, or expressions arranged in rows and columns. Each element in a matrix is identified by its position, typically denoted by two indices: the row number and the column number. Matrices are used in various fields, including mathematics, physics, and computer science, to represent and solve systems of equations, perform transformations, and manage data. Matrices can be added, subtracted, and multiplied, following specific rules. The size of a matrix is defined by its dimensions, such as 2x3 for a matrix with 2 rows and 3 columns. They are fundamental in linear algebra and are essential for operations in machine learning and graphics.