But it's not.
A binary prefix is that rare thing, an entertaining computer term. You see, a binary prefix is a way of expressing a number where, until fairly recently, you couldn't tell what, er, the number actually was.
I do love it when nerdy people manage to make themselves look ridiculous.
A binary prefix is used to describe the size of a kind of computer memory (it's RAM). Examples, historically, of these binary prefixes are the kilo[byte], mega[byte] and giga[byte], and the number they represent will be a one calculated by multiplying a certain number of twos together. For instance, a gigabyte is 1073741824 bytes, that number being a row of ten twos all multiplied together.
If you're counting something other than RAM then the prefixes kilo- mega- and giga- mean more or less the same thing as they do if they are being the aforesaid binary prefixes, except rounded to the nearest thousand or ten thousand or few billion or so.
A gigabit, for instance, consists of 1000000000 bits, as opposed to the 1073741824 in a gigabyte as mentioned above.
Rather sadly, computer people have now sorted this out. Kilo- mega- and giga- etc now always mean the whole thousands (so they are no longer binary prefixes at all). If you want a binary prefix, ie one based on a multiplication of the number two, then you are supposed to use kibi- mebi- or gibi-.
It's very sensible, and definitely needed.
But it's rather a pity, all the same.
Word To Use Today: kibibyte? Everyone will think you're talking about some sort of a dog biscuit, but that would be fun.