Entropy coding is a data compression technique that reduces the size of data by encoding information based on its frequency of occurrence. It assigns shorter codes to more frequent items and longer codes to less frequent ones, which helps minimize the overall amount of data needed to represent the original information. This method is commonly used in various applications, including image and video compression. Two popular types of entropy coding are Huffman coding and Arithmetic coding. Huffman coding creates a binary tree to assign codes, while Arithmetic coding represents the entire message as a single number in a specific range. Both methods are effective in improving data storage and transmission efficiency.