As with the term 'unlimited' to the average man in the street it means exactly that. Un known to everyone else the ISP's have many definitions of unlimited broadband....
Unlimited (but only for a short period)
Unlimited (but only if you don't go over your limit)
Unlimited (fair usage, but we don't define what fair usage is)
Unlimited (until we change our minds)
Unlimited (is really a finite number but we will let you know)
Unlimited (do you honestly believe there is such a thing)
Unlimited (we tied you into a contract so fcuk you when we change the rules)
Unlimited ( it was in the small print, page 1323, section 895 subsection 55, para 69, appendix 3 and if you failed to read it, well it's tough cheese)
So the moral of this is ISP's lie through their teeth, and will say anything to entice you in because that is the way they do business.
Oh have you heard the one about their promised 8GB broadband speed?