If you take quantum field theory as an example, the framework will tell you how to deal with fields and use them to calculate, but you still need to specify what fields are, the interaction between them and so on. .
One such theory is the standard model of particle physics, which is a quantum field theory. It describes how strong, weak and electromagnetic fundamental forces work, substances made of particles and how they interact. There are many other quantum field theories, but so far, the standard model is the theory that can best describe the universe we live in, and it has been confirmed with very high accuracy in experiments.
AdS/CFT correspondence assumes that some specific types of string theory (anti-De Sitter or ADS for short) described in a specific geometric structure and some specific types of quantum field theory belonging to a specific category (conformal) are double-domain theory, CFT for short.
In this case, the meaning of "double" is more or less that some parameters in "batch" (ADS space) correspond to some parameters on the boundary of this space (CFT).
Any string theory must have duality for some quantum field theories (and vice versa), which is of course incorrect. In fact, only a few pairs of theories can use AdS/CFT correspondence, and there is no known case that there is no string theory in AdS space and/or the quantum field theory that is not CFT is dual. So are you.
More generally, the holographic principle assumes (roughly) that for any quantum gravity theory (not limited to string theory; There are other theories), there should be some duality between the space volume described by quantum gravity theory and the space described by quantum gravity theory. Some theories describe a volume boundary without gravity (not necessarily CFT).
The main motivation of this hypothesis comes from the semi-classical (that is, "semi-quantum") treatment of black holes, especially the discovery that the entropy of black holes is proportional to their surface area rather than their volume.
Up to now, AdS/CFT correspondence is the only concrete example of holographic principle. Unfortunately, neither advertisements nor CFT describe anything similar to the real world. However, AdS/CFT is a surprising result in many theoretical applications.
We have every reason to believe that the holographic principle is also applicable to the real world to some extent-the universe we live in-but unfortunately, there is no evidence yet. Therefore, the discovery that really describes the similar correspondence between our theory of the universe and another theory may be the most incredible theoretical discovery in recent decades.