Speaking stops
Organ stops that control an actual rank of pipes, as opposed to mechanical stops such as couplers.
What it means
Speaking stops are the stops of an organ that bring an actual rank of pipes into sound, such as a Principal 8′ or a Flute 4′. The term distinguishes them from mechanical stops, which change how the organ is played but produce no tone of their own.
Musical use
The mechanical stops are chiefly the couplers, which link one manual to another or to the pedal, plus devices such as the tremulant or swell in some classifications. Specification lists and stop counts usually give the number of speaking stops separately, since only they represent the organ's actual pipe count. Speaking stops are thus distinct from couplers, which are drawn like a stop but merely add existing ranks from another division rather than sounding pipes of their own.
Performance practice
When reading a specification, check whether a quoted stop count includes couplers or not — this changes the apparent size of an instrument considerably. For registration itself, what matters is simply how the speaking stops combine.