What is a 'Screen Name' in Thunderbird's and SeaMonkey's address books?

[Detlef Lechner]

Avi Greenbury wrote:

> AOL Instant Messenger is an Instant Messenger system created by AOL.
> 
> An AIM user's screen name is the name by which other users of the
> system may find them.
> 
> http://en.wikipedia.org/wiki/Instant_Messaging
> http://en.wikipedia.org/wiki/AOL_Instant_Messenger

I still do not understand what this has to do with the free E-Mail
programs Thunderbird and SeaMonkeys address book.

Regards,
Detlef lechner