What is the best description of an isolated system?

There are many definitions and descriptions of isolated systems, and here are some of them:
1. it can be a physical system which is located very very far from all other systems, so there is absolutely no interaction between them, thus making it isolated
2. it can be a thermodynamic system with rigid walls, which prevents mass and energy to pass through

Iwould say false, not positive but if prices went up for both stores, technically there will be less buyers?