The term has arisen in connection with an encoder used in a device for measuring the angular velocity or velocity of a moving part and for detecting the direction of motion of the moving part.
The only way you can get information about encoders and forms used by encoders is through the Google Search. Access the results list and browse the available websites. You will find information related to different types of encoding. From cryptography to video encoding and codecs.
Google Search results: http://goo.gl/UTS4RR