difference between tone and build

[Eway]

"It is not necessary to move heavy weights in order to tone the muscles. Indeed, if toning rather than muscle-building is the aim, then instructors advise that a moderate circuit of a range of equipment is made no more than three times a week."

Isn't muscle-toning the same idea as muscle-building ?
Besides, what does it mean by making a "circuit" of a range of equipment?

[curmudgeon]

No, muscle toning is getting your muscles into shape, making them work better.

Muscle building is increasing the size, making them bigger.

[MikeNewYork]

"It is not necessary to move heavy weights in order to tone the muscles. Indeed, if toning rather than muscle-building is the aim, then instructors advise that a moderate circuit of a range of equipment is made no more than three times a week."

Isn't muscle-toning the same idea as muscle-building ?
Besides, what does it mean by making a "circuit" of a range of equipment?

A circuit utilizes a number of machines designed to work on different muscle groups.