They are the percentages of nitrogen (N), phosphorus (P), and potassium (K).
The N is total N, including all "fixed" nitrogen from nitrate, ammonium, urea, or other organic N compounds. By the way, that's organic as in the chemistry definition; containing reduced carbon. The specific form of N is important. For normal plant growing, N is best provided as ammonium or, better still, an organic (urea or whatever) form. Guano would be one.
Ammonium and organic N are fairly immobile in the soil and don't wash away as readily as nitrate. But the drawback is the organic forms require microbes to degrade them into nitrate or ammonium, which plants can use.
Most of us grow orchids in fairly biologically inactive places, whether a pot of bark or a cork mount or whatever. So the common wisdom is we can't rely on microbes to transform organic N into something our plants can use. So a proper orchid fertilizer will have little to no urea and all the N will be in the form of nitrate or ammonium.
So, even though I'm an organic gardener in almost every other way, I primarily rely on "chemical fertilizers for orchids. I do use some fish emulsion during the summer, but other wise use evil chemical fertilizer
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