What does the semicolon (";") mean in "$a\in(2;3)$"? I'm working on a linear program and I have the following constraint:

I'm wondering what does the ";" mean? At first I thought it meant the variable $a$ can only be $2$ or $3$, but that's what $(2, 3)$ is for, right?

The open interval of numbers between $a$ and $b$ is often denoted as $(a,b)$. However, in some countries where comma $(,)$ is used as decimal points, a semicolon $(;)$ may be used in place of a comma as a separator to avoid ambiguity: for example, the open interval from $0$ to $1$ would be written as $(0;1)$.
In the example above $a\in(2;3)$ means that $a$ is an element in the open interval from $2$ to $3$. 
