Adaptive Huffman coding
Adaptive Huffman coding is a class of data compression algorithms based on Huffman coding.
Adaptive Huffman is also known as dynamic Huffman, but dynamic Huffman is sometimes used more generally, to mean something like "any format in which the Huffman codebook can be changed".
With adaptive Huffman coding, the Huffman codebook is not stored in the file. Instead, it is constructed and re-optimized automatically as each successive encoded symbol (e.g. byte) in a stream is compressed or decompressed.