What does "toning" actually mean?
As used in fitness marketing, it means very little — there is no physiological process by which a muscle becomes "toned" as distinct from becoming larger or the fat over it becoming thinner. The appearance people are describing has two components, and neither is what the word implies.
What the look actually consists of:
Muscle size. Some muscle must exist to be visible. Building it requires resistance training with progressive overload — the same process as "bulking", differing only in degree and duration.
Body fat level. Definition appears when the fat layer over the muscle is thin enough. This is determined by energy balance over time, not by any particular exercise.
That is the whole explanation. "Toned" describes a moderate amount of muscle with relatively low body fat, achieved by exactly the same means as any other body composition change.
The specific myths the word carries:
Light weights and high repetitions "tone" while heavy weights "bulk". Both build muscle; heavier loads are generally more efficient for strength, and higher repetitions to near-failure also build size. Neither produces a different kind of muscle.
Women will accidentally become bulky. Building substantial muscle is slow and difficult for everyone, and the hormonal environment makes it slower still for most women. It does not happen by accident.
Specific exercises "tone" specific areas. Spot reduction does not work — you cannot preferentially remove fat from where you exercise, which has been tested repeatedly.
Muscle "tone" has a real meaning elsewhere. In medicine, muscle tone refers to the resting tension in a muscle maintained by the nervous system — which is clinically important and has nothing to do with appearance.
What to do instead of pursuing "tone": train the whole body with resistance two or three times weekly, progress the load, manage energy intake over months rather than weeks, get enough protein, and expect the timescale to be seasons rather than weeks. The programme is the same whatever word is used to sell it.
General information, not medical advice.