Diffusion

Diffusion is concerned with the spreading of the plaintext redundancy in the ciphertext. A cryptographer may want each digit of the plaintext and each digit of the key to influence many digits of the ciphertext to achieve this.

References

L. R. Knudsen, M. J. B. Robshaw, The Block Cipher Companion. Springer, 2011.
A. Menzes, P. van Oorschot, and S. Vanstone, Handbook of Applied Cryptography. CRC Press, 1996.