This lecture covers elementary matrices, which are used to perform elementary row operations on matrices. The instructor explains the types of elementary matrices and their operations, such as exchanging rows, multiplying a row by a constant, and adding a multiple of one row to another. The lecture also discusses how elementary matrices are used to obtain a matrix by performing a single elementary operation. Additionally, the lecture demonstrates the application of elementary matrices in matrix algebra, including their role in matrix inversion. The importance of elementary matrices in linear algebra is highlighted, emphasizing their role in matrix transformations and solving systems of linear equations.