What is the term for a value that is directly dependent upon other values? Say you have variables A and B, both of which express a certain quantity. Now let's say you have X, which equals the sum of A and B. For example, A = 10, B = 5, and X = 15 because 10 + 5 = 15. The value of A and B can change, so if A = 2, X = 7. So the value of X can also change, but only by the extension of a change in the value of one of the variables contributing to the value of X. In other words, A and B can 'freely' change, but X is 'locked' if you will.
To give a real-world example, let us say that A and B represent a number of Apples. If A = 10a, and B = 5a, and X equals the number of total apples. However, unlike values A and B, we can't really perform maths with the variable X to derive values significant of the real world, you can't take X and add it to A and state that we now have 15 + 10 apples. Mathematically no laws have been broken, but in terms of applied maths, this is not allowed, because you can't just create 15 apples from thin air. So whereas A and B would represent real-world objects, value X is more an abstract value that's derived from the sum of two other values.
My first thought was to call X a reference to A and B, but you could say that A and B are referencing a number of apples. Abstractions is another term, but you could also say A and B are abstractions of real-world quantities, in place for them, where X is an abstraction from abstractions A and B.  Maybe 'free variables' and 'locked variables' would be better? Though am not too sure. 
 A: I think what you're describing is just a mere illusion. You CAN change the total number of apple, by putting more apple in. It will force one, or both, variables to change, depending on how you do it.
To make this analogy clearer, imagine you're talking apples held by 2 people. Can you manipulate directly the number of apples held by someone? You might say yes, just give them apples, but I can argue that no, you're just changing the amount of apples hold on their specific hand, and that indirectly cause the total apple hold by that person to change.
In the end, what you have is just a relation: A+B=X. Or to write it in a more symmetrical manner: (1)A+(1)B+(-1)X=0. Three variables and a single relation between them. The 3 are dependent on each other by a single relation.
But there are terms like "independent variable" and "dependent variable" isn't it? These terms applies to the specific procedure (of doing experiment, etc.). Here there is some quantities that you can manipulate freely and monitor so that it has a specific value you want, they're called independent variable, while some other quantities are merely passively measured for their the value, they're called dependent variable. These terms refer to how you treat these quantities in your procedure: the one you set to specific values, or the one you just record.
So outside of that context, when you just have variables floating in empty space, such distinction no longer work. These are just a bunch of variables that dependent on each other by some relationships.
