This term describes a point at which a quantum computer can perform a calculation that a traditional computer could never complete within its lifetime.
It's a desperately vexatious thing, that after all one's reflections and quiet determinations, we should be ruled by moods that one can't calculate on beforehand.
Second, any model that described the whole universe in detail would be much too complicated mathematically for us to be able to calculate exact predictions.
If space and time are continuous, then even a tiny piece of the universe has infinite points and becomes impossible to simulate with finite computing power.
It suggests that even if quantum computers can't currently tackle big computing challenges, they may be useful in optimising some real-world logistics in a big way.