A q-series is a type of mathematical series that involves a variable q , which is often a complex number. These series are used in various areas of mathematics, including combinatorics, number theory, and partition theory. They can represent generating functions and have applications in the study of modular forms and special functions. One of the most famous examples of a q-series is the Jacobi theta function, which plays a significant role in the theory of partitions and elliptic functions. q-series can also be connected to Ramanujan's work, where he explored their properties and applications, leading to deeper insights in mathematics.