This lecture introduces the concept of a sigma field generated by a collection of random variables, discussing the information contained in these subsets and the connection with the sigma field generated by subsets of omega. The instructor explains how to find the smallest sigma field that makes all random variables measurable and provides examples to illustrate the concept. Additionally, the lecture covers the relationship between f-measurable random variables and barrel-measurable functions, highlighting how the information generated by a function of random variables may contain less information than the original variables.