There's a set of vocabulary (or jargon) that comes with the internet. Most have a collective meaning: googling (searching), troll (that guy) and meme (something that's... a meme).
However, there are some words, especially those of a technical nature, that are used interchangeably. None more so, than network speed, bandwidth, and bitrate.
First and foremost, let's make this easier on ourselves by tossing out the word speed. Speed is a vague term that essentially encompasses both bandwidth and bitrate.
OK. Without that bit of linguistic deadweight, we can move on to define the definable:
The number of bits (all those 0 and 1s) that can be transferred or processed from one point to another in a set amount of time (usually one second). Basically, it's like a speed limit on a highway.
The total amount of data that can be transferred or processed at any one time (also, usually one second). As such, both bandwidth and bitrate are usually measured in Kilobits or Megabits per second. Think of it as the number of people your car can hold.
How They Relate
Let's use an analogy to illustrate how bitrate and bandwidth relate. If you have a 40 passenger bus going 60 miles per hour, you can carry 40 people 60 miles in one hour. However, let's say that you're on a different road in a little two-seater Lamborghini coupe and can travel 75 miles per hour (or how about 251 miles per hour). With the sports car, you can travel the same distance much faster but with far fewer people (2 people 251 miles in one hour).
The same is true for bitrate and bandwidth. The more bandwidth you have the more bits (a higher bitrate) you can push through.
A note to all those non-Americans out there: please excuse our strange, illogical methods of measurement. Nonetheless, the concept still remains the same.
Bandwidth is the capacity and bitrate is the transfer rate [source]
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