What is the math symbol for between?

Answer 1

There is no single symbol.

Usually if x is between y and z then the notation used is x belongs to yz. In very simple cases, "belongs to" may be denoted by y < x < z [y is less than x and x is less than z] but that is only possible if there is an unambiguous ordering of the 3 values. If these are three points in 2- or 3-dimensional space, it will usually not work.

In such cases, the set notation of belonging is used. Given the pathetic nature of this browser, I cannot use foreign characters, but:

if e denotes epsilon, (the symbol which looks like that for the Euro, but with only one horizontal line) then the notation is x e (y, z) if x cannot be y nor z. For closed intervals the square brackets [] are used.