I have been studying sets, and on a website I do not normally use, I came across a notation I do not understand. It can be viewed here. If you need more information, it is from this wikipedia section.
What I do not understand is the uppercase $B$, as well as the meaning of the "$n;$". I've looked the up the "$n;$" part, but all I can find is that this is the "output" of the "$1/n$" part, which seems redundant.
Sets are used throughout mathematics. When you see an expression for a set, you have to know how that expression was defined. Writing out an expression without context and without definition results in a string of nonsensical symbols.
So, when you see an expression such as $B(n;1/n)$, you need to ask yourself: Where is that expression defined? If it was not defined, it's nonsense. Assuming it was defined, you have to read backward from where you saw it, until you find the definition. If you do that, you will find the definition of $B(p;r)$ a few lines earlier on that Wikipedia page.