Specifically, it is also used to denote 16′ stops which do not play below tenor C.
The most common example of this is the Vox Humana, which on theatre organs is usually a 61-note rank, but commonly available at 16′ and 8′ pitches. The 16′ stop is derived from the 61-note rank, but as there are no pipes below CC, the 16′ stop does not speak below Tenor C (see fig. 1). Such a stop would be labelled “Vox Humana 16′ tc”.
It is frequently useful to be able to include colour reeds and strings at 16′ in the ensemble, to add harmonics without use of the intra-manual couplers (Octave, Sub-octave); the absence of the 16′ octave in such cases is not normally a disadvantage.