In telecommunication, a convolutional code is a type of error-correction code in which (a) each m-bit information symbol (each m-bit string) to be encoded is transformed into an n-bit symbol, where n >m and (b) the transformation is a function of the last k information symbols, where k is the constraint length of the code.
Note: Convolutional codes are often used to improve the performance of radio and satellite links.
Source: from Federal Standard 1037C