The speed of light almost always refers to c. It would technically be correct to refer to any speed that light travels at as “the speed of light” but given the common name of c, that is almost never what people mean or understand by the phrase “speed of light” unless it’s been very clearly specified.

The speed of light through air is very, very close to c. The speed of light through fiber optics isn’t. Still a high percentage of c so very fast, but not a value that you’d ever mistake for c. With air it’s practically a rounding error away.