Hamming, Richard: (1915-1998) A mathematician who worked at Bell Telephone Labs for most of his life. For more details, see : http://en.wikipedia.org/wiki/Richard_Hamming

Hamming codes: 

A family of linear codes all of which have minimum distance d = 3. For each integer m > 1 there is a code over GF(q) with parameters: [n = (qm − 1)/(q-1),n − m, 3]. The parity-check matrix of a Hamming code is constructed by listing all non-zero columns of length m that are pair-wise distinct as elements of projective space.

Hadamard matrix:

One definition: A Hadamard matrix H of order n satisfies

H^{\mathrm{T}} H = n I_n \

where In is the n × n identity., so \det H =\pm n^{n/2}.

Another definition: A Hadamard matrix is a square matrix whose entries are either +1 or −1 and whose rows are mutually orthogonal.

* For tables of inequivalent Hadamard matrices: http://research.att.com/~njas/hadamard/

* For general information: http://en.wikipedia.org/wiki/Hadamard_matrix

Hadamard code:

This is a linear binary [2n, n + 1, 2n − 1] code using a Hadamard matrix of order 2n. If H is an Hadamard matrix of order 2n the codewords are constructed by taking the rows of H and −H as codewords, where each −1 is replaced by 0. In this way 2n + 1 codewords are constructed that each have a length of 2n.

* For general information: http://en.wikipedia.org/wiki/Hadamard_code