This lecture covers the concept of inversion in geometry, focusing on the relationship between points on a disk and their inverses. The instructor explains how to find the inverse of a point with respect to a circle, demonstrating the construction process and the properties of this geometric transformation. The lecture also delves into the power of a point with respect to a circle and how it can be used to construct orthogonal circles, leading to a non-Euclidean geometry model with unique properties.