BitDave’s right, but let’s clarify it all.
We have two different units here: bits, and bytes.
A bit is a BIinary digiT (Cute, huh?) In representational terms, it’s either a one or a zero, since it’s binary and can therefore have only two states. In electrical terms it’s either a higher voltage or a lower one. In some systems it’s either on or off.
A byte is eight bits. Why? Historical reasons, closely related to telegraphy. And it really doesn’t matter. Eight was the minimum necessary, and was reasonably convenient, and it’s far, far too late to change things now. It’s what’s used. Deal.
When it comes to bandwidth, what we’re talking about is transmitting information over a specific time, arbitrarily, the second. So many bits per second, or bytes per second. You use the one that’s most meaningful for whatever you happen to be doing with the information. These days, for most systems, bits aren’t terribly useful, while bytes are.
Being careful about the limitations of analogies, you can think of a bit as a letter, and a byte as a word. Now forget it, that’s a terrible analogy. So think of morse code. Dots and dashes used to indicate letters. It’s the letters that are useful. Now forget that analogy too. A single dot is the letter “E” and a single dash is the letter “T”. Funnily enough, those are the two most commonly-used letters in English.
Today’s tech moves very fast, so now we speak of kilobits and kilobytes, to deal with actual quantities. That is, “thousand-ish” quantities of each. Not exactly 1000 but close, and we won’t go there now.
If you’re a marketer, though, you love the kilobits, because they make things sound so much larger. That’s how they’ll sell you your home broadband connection - “it’s a million bits per second!!1!”. Which it is, yes, but it’s more useful to express it as 125 kilobytes per second since bytes are the useful quantum for computers. Doesn’t sound as impressive, though.
Sadly, we don’t widely use greek letters for this stuff anymore, so we abbreviate bits as “b” and bytes as “B”, to the everlasting confusion of the lay public. If you don’t know that b/s is way different from B/s, you may believe it’s all bs (sorry) and doesn’t matter.
But you also won’t particularly notice, and won’t be really careful about whether it’s b or B. You have to be careful when you’re calculating with them or communicating about them though. So case matters. It matters a lot.
And one point that I didn’t emphasize enough: all this talk about upstream speed is because it will directly and dramatically affect your downstream speed.