Later (after transmission or simply storage) the stream can be decoded again in almost the original stream.
In fact, codec means "coder/decoder".
Usually there is a loss of data, and better the codec, better is the result.
Now follows a list of the known video codecs:
codecs page 1 (_BIT to CYUY)
codecs page 2 (D26n to FVF1)
codecs page 3 (GLZW to MP2*)
codecs page 4 (MP41 to SMC)
codecs page 5 (SMSC to VLV1)
codecs page 6 (VP30 to ZPEG)