concept

Redundancy

In information theory, redundancy is the predictable part of a message - the part that carries no new information. English is heavily redundant: you can still read "th_s s_nt_nc_" with letters missing, because the rest is enough to infer the gaps. That redundancy is both waste and salvation: it allows compression (throw away the predictable part) and error correction (add controlled redundancy back to fight noise). A perfect copy across a noisy channel is bought with exactly this deliberate redundancy.