[goestin]

If my memories serves me right it was meant to be "Copy Convert" but "cc" was already taken for "C Compiler" so they went to the next letter in the alphabet (alpha beta), hence "dd". Thanks for listening to my TED talk of useless and probably false information :)

edit: i will be stealing disk destroyer, though

[axiolite]

    According to Dennis Ritchie, the name is an allusion to the DD statement found in IBM's Job Control Language (JCL), where DD is short for data definition  https://en.wikipedia.org/wiki/Dd_%28Unix%29#History