Classical Physics:

What "classical physics" refers to lie on the context? When discussing particular relativity, it denotes to the Newtonian physics which preceded relativity, i.e. the main branch of physics based on principles and rules developed before the rise of quantum and relativity mechanics. When discussing basic relativity, it denotes to the result of changing Newtonian physics to incorporate special relativity. When discussing quantum mechanics, it denotes to non-quantum physics, adding special relativity, and basic relativity.

Classical theory has at least two different meanings in Physics:

In the aspect of quantum mechanics, "classical theory" denotes to theories of physics that do not need the quantization paradigm, mainly Newtonian mechanics (which is also called as classical mechanics). Basic relativity and special relativity are also denoted to be "classical" in this sense.

In the context of special and general relativity, "classical theory" denotes to classical mechanics, and other principles which obey Galilean relativity. Light and other electromagnetic process cannot be correctly modeled in that kind of theory. Traditionally, light was resigned with classical mechanics by taking the existence of a "stationary" medium through which light goes through the aluminiferous anther.

The existence of these two diverse meanings of the term may lead to confusion: special relativity is a "classical theory" in the first time, but its predictions are more precise than "classical theory" in the second definition.

In other term, "classical theory" will have different meanings-if a current accepted theory is considered to be "modern" and its introduction shown a major paradigm shift, then last theory (or new theories lied on the older paradigm) will usually be referred to as "classical".