Before I got into running my own company I used to work for a design and development firm where we hosted all of our clients websites. By far the term that came up the most that our clients didn’t understand was bandwidth, and unfortunately this usually only came to light when they got a rather high bill for grossly exceeding their bandwidth usage.
Essentially, bandwidth is the amount of data that you are sending back and forth between web browsers and the server where your website is hosted. Things that will use up a lot of bandwidth are videos, audio files, and high resolution image files that you are hosting on your server. Videos embedded from services like Youtube or Vimeo will not count towards your bandwidth usage, and are actually a great way to keep it down.
If you are shopping around for a web host you might notice that several of them offer ‘unlimited bandwidth*’ even on their cheapest economy and shared hosting packages for $5 a month or less. Sound too good to be true? Pay attention to that asterisk, because it’s unlimited so long as it doesn’t violate the Hosting Agreement (that 100+ page legal document that I’m sure you read very carefully). Nobody really names a hard data limit in their Hosting Agreement, they keep it pretty nebulous by saying something like ‘any amount that compromises the stability, performance, or or uptime of servers’.
All that being said, it is very unlikely that you will be in violation of your Hosting Agreement unless you are running a website where you will be storing and serving large files such as those mentioned above (video, audio, hi-res images) or you will be getting extremely large volumes of traffic. Even then there are strategies you can use to mitigate impact on your bandwidth usage such as using streaming services or content distribution networks. Or if you really need to you can get yourself a Virtual Private Server or Dedicated Server which will be able to handle your bandwidth needs. They are pricier than shared hosting, but less expensive than constantly paying for bandwidth overages!
Here is a video on how to set up MaxCDN which will help you keep your bandwidth usage down: