What on earth does :80 tell you on the end of a domain name??

I have a plugin on a lot of my sites that monitors ranking for keyword phrases as they are typed in.
Today I've had lots of notifications that the sites are ranking for mysitename.whatever:80, so obviously someone is going through them trying :80 on the end of them all!
I'm guessing that it tells you something about the site, but I have no idea what?
Could someone enlighten me please

Web servers run on port 80. If you type in http://www.yoursite.com:80 into your web browser it will bring your site up.

Port number. By default it is 80 so no need to use it, unless the server is listening to other port.

Oh, thanks for that, so it's just something automated then is it?
Still don't get why it's just happening today, but as long as I'm not getting a massive hack attack that's the main thing

Tabby22 said:

Oh, thanks for that, so it's just something automated then is it?

Click to expand...

Yes. I have no real experience in server administration, but I think the (default) port shouldn't be visible in the address line, if one just accesses the main domain?