Flue or what? :p

[boron]

What means "viral" in the context of adverising? I guess not a flu :p .

Next what means "opt-in" regarding mails. Is this that someone agreed to receive advertising e-mails?

[Mystic]

From Wikipedia (http://en.wikipedia.org/wiki/Viral_marketing)
Viral marketing and viral advertising refer to marketing techniques that use pre-existing social networks to produce increases in brand awareness, through self-replicating viral processes, analogous to the spread of pathological and computer viruses. It can often be word-of-mouth delivered and enhanced online; it can harness the network effect of the Internet and can be very useful in reaching a large number of people rapidly.

Some of the first recorded offline / online viral campaigns were developed by Tim Nolan of Spent2000.com fame circa 1996. By placing abstract pairings of catch-phrases, quotes, song lyrics and image mashups, Mr. Nolan developed a method of creating "buzz" around a URL based installation. Phrases like "This city isn't safe" placed along side a URL created curiosity enough in people's minds to remember a URL and visit again once they were online.

Eg. : What LOST did last year, with Lost Experience (http://en.wikipedia.org/wiki/Lost_Experience). Also Opera did something similar. Posting cryptic clues all over its website.

Viral marketing mainly uses word of mouth. It involves something intruiging, that makes the customers readily participate in it and spread the word (by telling friends, blogging about it etc).

[affiliate7]

- viral marketing is to publish some thing one and you give the right for people to send or exchange this. such as you write a free ebook about seo and you ask people to not change the content of this ebook and they use send to friend,...
- opt-in list: when you subscribe to newsletter or to download a free ebook or other you put your email adress then an email is send to your email to confirm that you accept to receive email from this web site or this person.
- opt-out list is list that the owner of this list collect from online any adress email from forums, FFA,... and the onwer of this email he/she never confirmed to accept that you send him an email.

the dirence reside that the person confirm to accept email from you and he interested to receive information from you.