kiora Spam is messages from a stranger, trying to sell you something or getting you to go to their website, or just being a damn nuisance.
like Some are just advertising, like the junk mail that comes through the letterbox, or the jokes and sentimental posts that do the rounds of emails, but some can be a deliberate attempt to trick you into revealing a username and/or password, which they can then use to pretend to be you.
They can then order stuff that you pay for, or get into your account to move money into theirs. They can be very clever, giving a link which goes to a copy they have made of a genuine bank website, where they ask you for your password - which goes straight to them.
If you get one which looks as though it is one of these, do not follow the link they give, but open a new browser window and go direct to your bank or other account and ask them whether they are trying to contact you.