NMEA stands for  <National Marine Electronics Association>, the organization that is responsible for the standardization of the exchange of data between marine instruments. “NMEA 0183 ” refers to the standardized data-format consisting of so-called NMEA sentences which contain data-strings in ASCII-code. Values are separated by commas and sentences are terminated by CR-LF, which makes them easy to display or print. NMEA 0183 also defines the electrical interface and the serial transmission method. A good source of general information about NMEA is the following webpage:

 vancouver-webpages.com/peter/nmeafaq.txt.