As with most things in life advertised as unlimited, there may be fair usage policies. So really, it's unlimited access, to a point. The good news is that these fair usage policies are incredibly generous, and it would be near impossible to hit them. Most also refresh after 24 hours. An example would be 500GB every 24 hours; even hours of Netflix will not surpass this.
Just remember to read the terms and conditions to understand the fair usage policy on bandwidth.