Huffman coding
Huffman coding is a way of encoding data. The method was developed in 1952, by David A. Huffman, at MIT. It was first published as A Method for the Construction of Minimum-Redundancy Codes, in 1952. The method is a prefix code, and a way of lossless data compression. The idea behind it is very simple: There's a dictionary that contains words, and how often they occur in the text. Each word is replaced by a variable-length code. Words that occur more often get shorter codes.  The codes must not overlap and be unique.