Complex sentence: In this equation, "C" is called the speed of second sound (i.e. the fictitious quantum particles, phonons) and this equation is known as the hyperbolic heat conduction (HHC) equation.
Split into simpler sentences: In this equation, "C" is called the speed of second sound (i.e. the fictitious quantum particles, phonons). The equation is known as the hyperbolic heat conduction (HHC) equation.