The chirp mass (Mc) is a function of the masses of two orbiting bodies that is related to the rate of energy transferred away through gravitational waves. Its role is somewhat like reduced mass: it encapsulates some calculation and is a relation between masses that some observations reveal.
Mc = ( m1 m2 )3/5 / ( m1 + m2 )1/5
The following differential equation approximately relates this value to the orbit's GW frequency and its rate of change:
Mc = c³/G(5/96π-8/3f-11/3df/dt)3/5
This is the equation solved for Mc in terms of f and df/dt, the latter two being the values that can be measured from observation. (I assume the name is chirp mass because these two values are evident from a GW chirp.) It is approximate because it is based upon the first term of a multi-term solution. Additional information is required to solve for the individual masses.