Unlimited bandwidth is just a marketing term to get more customers.
If you come across a web host that advertises unlimited bandwidth then your website will most likely be hosted on an oversold shared server.
Most websites especially ones on shared hosting will only use maybe 5 gb of bandwidth per month.
And that's what the unlimited shared web hosting companies are banking on. They know that you'll reach the servers other limits before you use too much bandwidth.
When you start going over 5 or 10 gb of bandwidth then you'll likely be needing a vps server or even a dedicated server.