spam: CAUBE's definition

Spam is any electronic mail message that is:

Transmitted to a large number of recipients; and

Some or all of those recipients have not explicitly and knowingly requested those messages.

It does not matter what the content of the message is. It can be an advertisement for a commercial product, a solicitation for donations by a charity, or a religious pitch by somebody intent on saving your soul. If it meets the two criteria above, it is spam.