How does BusinessDays.jl work?

I see in the BusinessDays docs that the package achieves its performance by using a cache. However, I don’t understand what a cache means in this context, and how does using one create superior performance to something like QuantLib in C++? Can someone please explain this to me?

It looks like once a date is determined to be a business day or not the result is stored in a dictionary so for the second time that date is checked no calculation is necessary. The ‘cache’ is the dictionary. So for lots of repeated checks that is much faster.