Discoverable: Refers to whether an interface feature can be discovered by the user without already knowing that it’s there. Things like tooltips aid discoverability; adding keyboard shortcuts without showing them to the user anywhere is a common example of bad discoverability.
Hue, Saturation, Value: Hue, Saturation and Value (HSV) are a different way of measuring colours (as opposed to say, RGB: Red, Green, Blue). Hue is what we generally think of as colour: blue, green, purple. Within those colours, you can also vary saturation, which is the vibrancy of each colour: in some sense, saturation is the distance from monochrome. And finally, you have value, which is essentially brightness or lightness. In interfaces, what is particularly important is that hue-only differences are some of the hardest for the eye to spot (and are most vulnerable to colour blindness issues). Here are a bunch of colour pairs which only differ in hue:
Value differences are among the easiest for the eye to see; here are some colour pairs which differ only in value:
Of course, when you stare at these pairs you can see the difference. But often in an interface, you need to make the difference obvious as the eye scans across the screen, without it needing to focus solely on your colours. Some of the hue pairs at the top tend to merge when you glance over them.
Intuitive: Horribly vague term over-used when talking about interfaces. Breathing is intuitive, everything else is learnt by prior experience. Talking about interfaces being intuitive makes it sound like there is an abstract, natural way to compare interfaces, when practically it is usually about conventions. Having the cost of a card in the top corner, or having a back button in the top left is not more intuitive than any other option, it just fits in by copying prior conventions. If you see me use this term, complain.