If you describe a situation as a theoretical one, you mean that although it is supposed to be true or to exist in the way stated, it may not in fact be true or exist in that way.
双语例句
例： This is certainly a theoretical risk but in practice there is seldom a problem.
这在理论上肯定有风险，但在实践中却很少出问题。
例： These fears are purely theoretical.
这些恐惧纯属理论上的。