I've read quite a few other answers on this site such as this one, but can't quite seem to understand fully yet.
Say we have a container with gases reacting such that the number of moles on both sides of the equation are not equal. If we then, for instance, reduce the volume of the container, the total pressure increases and the value of the quotient Q will also change. The net reaction then favours a particular direction so that the mole fractions change sufficiently for Q to return to the value of K, which remains constant.
This is commonly described by saying equilibrium shifts to either the left or the right. Whilst it is true that after the system has again reached equilibrium the mole fractions have changed (so in a sense, the new equilibrium has shifted to one side in terms of number of moles), the value of Q is equal to its initial value so in this sense the position of equilibrium as defined by K has not changed.
The same applies to changing the concentration of a species; the actual concentrations of every species after the system has re-equilibrated will be different, however the value of Q will have returned to its previous value.
The only situation that I can think of where the position of equilibrium actually shifts is when a change in temperature alters the value of K.
My question is, essentially, is the term 'position of equilibrium' more of a qualitative descriptor of the composition of reactants and products? I initially thought it meant the value of Q at equilibrium (or K), but evidently in gaseous reactions the equilibrium yield does change with changes in pressure though K remains constant, so such a definition would not work.