What is the "opposite" of a random variable? I am learning about random variables with all of their different types of distributions for discrete and continuous types. However, before knowing about random variables, I am not sure what would be a variable in statistics which is not random? Is not every variable by chance and everything already a random variable? What would be the "opposite" of a random variable i.e. some variable which is NOT to happen by chance? 
 A: One thing that might be worth noting is that in the formal definition, a random variable is a function -- in particular, a measurable function  $X: \Omega \to E$ from a set of possible outcomes $\Omega$ (which is in fact a probability space -- more here) to a measurable space $E$. 
Along the same lines of @gunes answer (+1), it doesn't quite make sense to discuss the opposite of a function -- you could say it's a constant, but how would you consider a function such as $f(x) = 0$? Is it "more" constant than other functions? It's a bit like comparing apples and oranges, since functions and scalars are very different types of objects. 
I think your question is more around the use of the word "variable", which can be a bit confusing. For instance, in algebra you might encounter a problem such as "Find the roots of the equation $x^2-9=0$". Here, $x$ is a "variable", but it takes on a deterministic value (namely, $ x = \pm 3$ ) and can really be considered scalar since $x \in {\Bbb R}$. There's no presumption of it representing a relationship between some event and an associated probability, so it's not considered a random variable. 
A: A non-random variable is generally called a Constant.  But constants are not really the opposite of random variables, in the same way integers are not the opposite of real numbers - they're a subset.
A constant is just a random variable with all it's probability mass concentrated at one point.  (i.e. it has a Dirac-delta function for probability distribution)
A: A random variable which is not actually random, and doesn't change by chance, is by definition a constant. But, it is still a RV. Since the RV definition is a superset of constant RV definition, I believe there is no conceptual opposite.
A: I would say a deterministic variable.
Examples:
Random variable- the amount of heads when a coin is tossed 100 times.
Deterministic variable- the age of the Eifel tower in exactly 12 years from now.
