This lecture discusses the use of the enum keyword to define a set of integer constants in programming. It begins by explaining the concept of literal constants and how enums can represent various categories, such as fruits and colors. The instructor illustrates this with examples, defining enums like Fruit with values such as POMME, POIRE, ABRICOT, CERISE, and ORANGE, and Couleur with ROUGE, VERT, BLEU, JAUNE, and BLANC. The lecture emphasizes that the first constant in an enum is always assigned the value 0, with subsequent constants incrementing by 1. Additionally, it covers the option to initialize constants with specific integer values, as shown in the example of months. The instructor highlights the practical benefits of using enums, such as improving code readability and facilitating the use of these constants in switch statements. The lecture concludes with a discussion on the conventions surrounding the use of enums in programming, particularly in relation to switch statements.