A dense matrix is a type of matrix in which most of the elements are non-zero. This contrasts with a sparse matrix, where many elements are zero. Dense matrices are commonly used in various fields such as mathematics, computer science, and engineering, particularly in linear algebra and numerical analysis. In a dense matrix, the data is typically stored in a two-dimensional array format, allowing for efficient access and manipulation of the elements. Operations like addition, multiplication, and inversion can be performed easily, making dense matrices suitable for applications in machine learning, image processing, and scientific computing.