World Class - I see this advertised but never seen it defined. I think of these specimens as exhibiting exceptional quality and presents, such that any major mineral collector would be tempted to acquire them - specimens a major museum would want to obtain. I do not believe price defines a World Class mineral specimen but World Class specimens do command higher prices.
Investor Grade - While there are a number of factors that make a mineral an investor grade piece it is mostly about perfection and aesthetics; rarity of course also plays a roll.
Collector Grade - Usually, a visually pleasing mineral and a good example of the mineral species/type/form. While the specimen may contain fractures, repairs, etc. the overall quality of the piece makes up for them.
Display Grade - any mineral that looks pleasing in a display case.
Specimen Grade - lacking display value these minerals are primarily of interest as an example of a mineral species or type. These are acquired as study pieces. Some really rare minerals may only be found in specimen grade, and as such, some might consider these investor grade minerals as well.
A collector with a focus on mineral varieties, as apposed to ascetics, might view many specimen grade minerals as collector grade minerals.
In many ways the above grades are very artificial in that one might acquire an investment piece for display and it may also fill a species vacancy in ones mineral collection. The above grades really reflect how a dealer might classify a mineral to target it to a specific mineral buying group.
Defining High End - In the articles on buying minerals I used the term “high end” to describe a category of minerals. “High end” is a mushy term to describe a mineral. Everyone has their own view as to what constitutes a high end specimen. Some people call anything out of their price range as high end. Others might look at a low priced but exceptional quality mineral as being in the high end of specimens. A few dealers of highend material consider any thing with a price tag of $35,000 or more, highend. I usually use the term “highend” to decribe exceptional quality specimens; regardless of price or value.
Next - Displaying your minerals to make them look good.