Physics is the part of the generating function of reality that is responsible for its lawful structure. Any world of observations is compatible with an infinitude of generating functions, but the truest and likeliest physics is imagined to be captured by the shortest possible program which compresses and can regenerate all of reality's regularities. The incompressible features of an observed reality are usually considered indexical information or an initialization seed rather than part of physics.
"Base physics" may be said to unambiguously refer to the physics of base reality, rather than of virtual or hypothetical realities. However, the scope of base "reality" that the question of physics should pertain to is unresolved, with some refusing to even admit Everett branches decoherent from their own and others welcoming realms generated by all possible mathematics.
"Physics" also refers to the problem and the discipline of figuring out physics.