Theano is a powerful Python library designed for efficient numerical computation, particularly in the realm of deep learning. It serves as a foundational framework that allows developers to define, optimize, and evaluate mathematical expressions involving multi-dimensional arrays. Theano can leverage both CPU and GPU resources, making it suitable for handling complex computations efficiently. While it can be used directly, many developers prefer to utilize wrapper libraries like Keras or Lasagne, which simplify the process of building deep learning models by abstracting away much of Theano’s syntax. Despite no longer being actively maintained, Theano remains a valuable tool in machine learning and data science.