Electronic mail and Junk e-mail

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.

Junk e-mail and electronic mail are semantically related. In some cases you can replace phrase "Junk e-mail" with "Electronic mail", this phrases are similar.

Junk e-mail noun - Unwanted e-mail (usually of a commercial nature sent out in bulk).

Electronic mail and junk e-mail are semantically related. You can use "Electronic mail" instead a noun phrase "Junk e-mail".