Is there more than one definition of natural selection?

I hope you don't mind me jumping in as well.
I'm sorry if I'm stating what you already know, I would just like to clarify what you meant when you said 'NS seems to have a zero or rest state, and it seems to have an active state with variation of activity'.Anyway in both this and the previous thread, natural selection seems to repeatedly be referred to like an entity in itself, deciding what to smite and what not to smite. I've always regarded it as a collective term for the various obstacles organisms have to overcome in order to survive and pass their genes to the next generation, for example the availability of food/water, predation or disease.Now if the organism fails to overcome these obstacles it will die, effectively ending it's opportunity to pass it's genes to the next generation. If it fails to attract a mate, it won't necessarily die, but the outcome is the same in that it has failed to pass on it's genes.
Now which factors have the greatest selective pressure depends on the organism and the environment it exists in i.e. not all selective pressures apply equally and some may be non-existant for a particular scenario. In a harsh environment, a desert for example, the main selective pressure may be lack of food/water and the majority of organisms in a generation will die before getting a chance to mate. In this case attracting a mate (i.e. sexual selection) is a low selective pressure due to fewer individuals surviving. Is this what you meant in the other thread when you defined sexual selection as something separate from natural selection?Now consider a scenario where other selective pressures are reduced, for example plenty of food or less predation. Under these circumstances competition to attract a mate increases, so this becomes the predominant factor in natural selection as to who passes their genes onto the next generation.Have I got this right? I know it's a bit over simplified, I've just not looked at this for a while.

The HW principle describes a theoretical equilibrium for genotype frequencies at a given locus. Calculating the HW equilibrium relies on eight different assumptions. The HW equilibrium does not describe what we see in the real-world because no natural population fulfils all the assumptions made in the calculation.
Note that any kind of selective pressure, not just sexual selection, can cause a departure from the theoretical HW equilibrium. This is the point of the HW principle, the extent to which real-world genotype frequencies depart from the theoretical equilibrium indicates the amount of selective pressure a specific gene locus experiences. It was never a description of real-world populations.