I'm not entirely sure I know what you mean.

As far as I know, some encryption algorithms (or "ciphers") use the key (of n bits) to encrypt the first n bits of data, then perform some transformation on the key (based on the bits of data just encrypted, and perhaps previous bits), then use that as the key for the next "n" bits of data, and thus repeat the process.

This ensures that the cipher proceeds with each block to a different key, so that repeated parts of the message are not encoded as a repeating sequence.

I really am clueless in this field, so please feel free to ignore or correct me