The Szegő theorem is a result in complex analysis that deals with the behavior of analytic functions on the unit circle. It states that if a function is analytic and bounded on the unit disk, then its boundary values can be represented in terms of its values inside the disk. This theorem is significant in understanding how functions behave at the edge of their domain. Additionally, the Szegő theorem has applications in various fields, including signal processing and control theory. It helps in reconstructing signals from their frequency components, making it a valuable tool in both theoretical and practical contexts.