This lecture covers the concept of eigenspaces in linear algebra, focusing on the definition of eigenspaces associated with a linear transformation and the diagonalization of matrices. The instructor explains how to determine eigenspaces through examples involving transformations, values, and vectors. Various properties of eigenspaces are discussed, such as being a vector subspace. The lecture concludes with practical examples of determining eigenspaces for specific matrices and values, showcasing the application of eigenspaces in solving systems of equations.