This lecture covers the concept of division euclidienne in polynomials, exploring the process step by step. Starting with the introduction of i as a solution to x² + 1 = 0, it delves into the classification of polynomials by their coefficient types and degrees, demonstrating how to perform division with remainder. The instructor illustrates the division of a polynomial P(X) by Q(X), showcasing the steps involved in finding the quotient and remainder. Through examples and explanations, the lecture emphasizes the importance of understanding the behavior of polynomial degrees during addition and multiplication.