Definitions for "Principle of equivalence"
A basic postulate of general relativity stating that it is impossible to distinguish locally between a gravitational field and an accelerating reference frame.
core principle of general relativity declaring the indistinguishability of accelerated motion and immersion in a gravitational field (over small enough regions of observation). Generalizes the principle of relativity by showing that all observers, regardless of their state of motion, can claim to be at rest, so long as they acknowledge the presence of a suitable gravitational field.
Einstein's declaration that a gravitational force cannot be distinguished from an inertial force; hence a gravitational field can be replaced by an accelerated system.