Electronic mail and Second class

Electronic mail noun - (computer science) a system of world-wide electronic communication in which a computer user can compose a message at one terminal that can be regenerated at the recipient's terminal when the recipient logs in.

Second class and electronic mail are semantically related. In some cases you can use "Second class" instead a noun phrase "Electronic mail".

Second class noun - Not the highest quality in a classification.

Electronic mail and second class are semantically related. Sometimes you can use "Electronic mail" instead a noun phrase "Second class".