To illustrate the concept of caches, let’s consider the following analog example from medicine:
Imagine a dental treatment or surgical operation. The doctor asks the assistant for a utensil, like a scalpel, disinfectant, or bandage. If the utensil has already been laid out, the assistant can immediately respond to the request and hand it over to the doctor. Otherwise, the assistant will need to locate the utensil in the medical cabinet and pass it to the doctor. After use, the assistant keeps the utensil close to hand for quick, subsequent reuse.
The individual utensils are not completely unrelated in terms of their use: For instance, if the doctor asks for disinfectant, they will likely also need a swab; a needle is also useless without sutures. The assistant will keep the associated resources available to minimize the time required to retrieve them.
As you can see, keeping resources on hand that are often needed or used together is a very useful, commonplace practice. In the digital world, these processes all come under the term “caching.”