Unlimited Bandwidth: what does it reeeeally mean?

I've heard lots of quotes: "there's no such thing as unlimited bandwidth".

Ya well... to the people who say that have you heard of F*sth*sts??
They give customers UNLIMITED bandwidth!

Erm... well... errr... I looked at the small print and it said something about having a restricted bandwidth of 128kbps or 256kbps or something really small like that.
I forget what the terminology was to describe this.

What this essentially means is that if you hit the jackpot and zillions of people coming to your website all hitting it at the same time: then you got trouble!
One painfully slow website.

Or... am I simply understanding things wrong?

250GB: being very vague and very very rough estimating: how many visitors to an 'average' website will this allow?

Thanks.


OM