Entropy: The amount of underlying information content of a message. For tutorial users familiar with compression programs, we can mention that if a message is (losslessly) compressible, it ipso facto has an entropy less than its bit-length. Take a simple example of a message with less entropy than its length might suggest. Suppose we create a database field called "sex" and have it store six ASCII characters. However, "male" and "female" are restrictions of the allowable values. This database field contains just one bit of entropy, even though it occupies 96 bits of storage space (assuming 8-bit bytes and so on).