Well with a high resolution medium (e.g. t-grained b&w film or very high pixel density sensors like the pentax Q) sharpness refers to the terminal resolution at which contrast drops below a threshold. Zeiss uses 10%, so when they give you lp/mm numbers like 400 for the 25 Biogon or 300 for the 100 MP that is what they are referring to. A lot of tests these days use MTF50, or what resolution contrast drops below 50%, as I believe this is the bases for how the imatest machines work.
Contrast is different than sharpness then. Contrast refers to transmission at various resolutions. "Macro" or "large structure" contrast is at low frequencies, like 5 or 10 lp/mm.
Optics are a compromise, and one of the compromises is how fast contrast levels fall off as you increase frequency. If you look at a lens like the v3 Summicron, Leica decided that they could sacrifice some of the contrast at high frequencies to boost it in the ranges that are important for what was considered a reasonable print size at the time. As films improved and enlargements got larger so too did the requirements for contrast at higher frequencies.
The human response to frequencies is not that great, frankly. When the research that ultimately led to the SQF measurements was done, they figured out that the impression of sharpness in a picture you were looking at from a foot was something in the neighborhood of .5 to 2 lp/mm. That makes 40 lp/mm only relevant at 20x enlargements, which probably goes a long way to explaining why people who eschew pixel peeping think a lot of not so sharp lenses are in fact pretty sharp.
Further compounding the issue is color separation and response in a lens. Lens makers have long battled with how to make two close colors be better differentiated. Frankly, Leica rules the roost in this regard, even above Zeiss. I can tell you that I am less intimate with the underlying issues here.
So why do people make up words? Because this a complicated subject and they need something general that speaks to their experiences without requiring them to read published articles on the frequency response of the human eye.