Electronic mail and Third 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.

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

Third class noun - Inexpensive accommodations on a ship or train.

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