describes: the phase relationship between two specified oscillations e.g. 
and 
that have the same angular frequency 
and which respectively involve phase constants 
and 
that differ by an odd integer multiple of 
so that 
where 
is any integer. The maxima of one oscillation then coincide with the minima of the other. [P5.1, P5.7, P6.1]
may also be applied: to waves at a common point (or possibly at separate points) by comparing the oscillations caused by the waves at the relevant point(s).
See phase relationship, in phase and out of phase.
Copyright 1997, The Open University