Email is a good mean of communication that everyone enjoys. In most cases it reaches you before a telegram!!!
You may say, "Kiruthik stop, everyone knows these things. What exactly you want to say".
Rite, coming to the point : Not only Advertisements / Unwanted / Junk / Bulk mails are SPAM.
Any email reaches the  inbox, which don't have anything to say or which is likely to be deleted while the user  looks the first line, is also a SPAM.

For example, you may Forward emails to your contacts for one or more reasons :

1. When you get a nice joke & like to share. Cool, you want everyone to be enjoy it.

2. When you get a informative stuff, a good example is here. Great, you are Generous!!!!!

3. When you get a nice Stills of a Porsche, or a BMW or something like, Love is... or Friendship means ....etc., this kind of similar stuffs. Then also, its Ok.

But...

4. When you forward a mail, which has something like : "Yahoo is going to shut down its messenger service", so please forward this mail to all the contacts you have in your list........::: Do you think Yahoo will close any of their service, if you break this chain of mail ????

5. When you get a mail like : "For every person that you forward this e-mail to, Bill Gates will pay you $245.00, for every person that you
sent it to that forwards it on, Microsoft will pay you $243.00 and for every third person that receives it, you will be paid $241.00.
Within two weeks, Microsoft will contact you for your address and then send you a cheque...." ::: Do you think, the richest man is a dumb like you ??

6. Or like : "A message with a Holy Place-Photo in the background, Forward this mail to 24 people you know within 24 hours, you will
get everything you like, or else your fate will chase. :::  Do you believe your Almighty is checking Email ????, if so let me know his email ID.

Do you think the last 3 are really going to happen???? I used to get nearly 10 mails a week like this. These type of mails are sometimes forwarded by a high profiled people in some MNCs. It really makes me to think of them & their mentality.

See, you are not a kid, who does whatever his friends do.

Please don't feel bad, if you are of this type. I'm telling this for your good. If someone is sending mails to you like this, then Forward them this Blog. May be my blog will get better visibility