Explore the fifth lecture in a series on braided fusion categories, focusing on Witt equivalence of non-degenerate categories and the categorical Witt group. Delve into advanced concepts in algebraic theory of semisimple braided tensor categories, also known as fusion categories. Gain insights into the structure and classification of these categories, which play a crucial role in quantum symmetries, topological quantum field theories, and representation theory of quantum groups. Suitable for graduate students, this 50-minute talk is part of a workshop on Quantum symmetries, Tensor Categories, Topological quantum field theories, and Vertex algebras held at the Centre de recherches mathématiques (CRM).