A Codec (coder-decoder) is a a piece of software that is used to compress or convert an analogue voice signal into a digitally encoded version that is ready for transmission. Once the data has been received, the receiving codec will convert the digitally encoded version of the voice signal, back into an analogue signal. Codecs, and the associated call quality can vary significantly following compression and transmission, which offers the organisations using them the flexibility to choose a codec that allows them to optimise the bandwidth and computational power that they have available.
A Codec is a technical term for the following variations, which essentially mean the same thing: compression - decompression / compressor - decompressor / Code Decode. In practice the compression and decompression is done by a computer program for the purpose of transmitting data over a data connection and allows them to be translated when they reach their destination. Within the telecommunications industry, the data transmitted through the Codec would be the packets of data that make up a call.