COder/DECoder or COmpression/DECompression algorithm.
A codec converts local analog signals into digital data, compresses them and transmits them to the destination system, that has to support the same codec. This remote codec receives the compressed digital data from far side, decompresses them and converts them back into analog signals. So, Quadro needs codecs to turn phone call signals into digital data in order to exchange them with the called party.
The codecs used in Quadro are - among other things - characterized by their data rates: the smaller the data rate is, the poor is the quality of voice and vice versa. The table Needed Bandwidth for IP Calls shows a list of all supported codecs and the correspondingly needed bandwidth.