The Discrete Cosine Transform (DCT) is a mathematical technique used to convert a signal or image from the spatial domain into the frequency domain. It helps in analyzing the frequency components of the data, making it easier to compress and process. DCT is widely used in image and video compression formats, such as JPEG and MPEG. DCT works by expressing a sequence of data points as a sum of cosine functions oscillating at different frequencies. This transformation highlights the most significant frequencies, allowing for efficient data representation and storage. By focusing on these key frequencies, DCT reduces the amount of data needed while preserving essential information.