The Fourier transform is a mathematical technique that decomposes a complex signal or function into its constituent frequencies. It is commonly used in a variety of fields such as signal processing, image analysis, and communication systems to analyze and manipulate signals and extract important information. The Fourier transform essentially converts a signal from the time or spatial domain to the frequency domain, allowing for easier analysis and processing of the signal's frequency components. It is a powerful tool for understanding and manipulating signals in a wide range of applications.