Email, e-mail or electronic mail is the transmission of messages (emails or email messages) over electronic networks like the internet.
I guess this dry definition is not what you've been looking for. And indeed, it doesn't say or mean much, not to me either. This "transmission of messages" could be anything. But don't let that intimidate or confuse you. Email is as simple and straight forward as letter writing.
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supermarket racks
fruit & vegetable racks
electronic racks