I believe you are correct - "transflective" is the combination of the two. A reflective backing to the LCD that allows you to read it in sunlight (if we ignore glare), but its somewhat transparent so it allows some light to come through so a backlight can be used in low lighting conditions. They're generally as good as reflective in bright conditions, but will absorb a fair bit of the backlight in low light conditions. Thats normally not a problem though since in very low light the backlight doesn't need to be bright at all, and you're better off under-driving them.
Note its very rare for transflective displays to be negative transmission, they are almost always positive - so it should be black/blue pixels on white/grey background, as opposed to negative,which is normally black display with pixels allowing light to come from the back. Negative displays always require a backlight.
FSTN tech adds a correction film to the display, so that pixels appear "black" instead of bluish, and it improves contrast - it has nothing to do with whether its sunlight readable, but its generally a nicer-to-look-at type. Like the old nokia 3310 phone - that was a classic graphic FSTN and easily read in full sunlight.
These days, whilst theres still millions of these types of displays used in many products, it is becoming harder for the hobbyist to find them. Sure there's still thousands of the HD44780 character displays, but the market seems to be flooded with either STN blue (white on blue, needs a white backlight, difficult to read in sunlight, and looks awful) or "green" which are actually VATN displays with a green filter on the back to emulate older STN displays. VATN displays surprisingly have very good contrast and I would think that even without a reflective backing can be read in sunlight easily. Given they are about $3 each, I would buy one and test it yourself if you need a 16x2 character display. The backlights are stupid efficient, needing a few mA to be pretty bright.
As for graphic, again, STN/FSTN is still about in 128x32, 128x64 all the way up to 320x240, but have mostly been displaced by TFT and OLED displays and so are harder to find, and expensive.
So briefly: FSTN or VA, both provide excellent contrast with VA also having a much wider viewing angle, but transflective is what you want. Definately a positive display, sometimes the white diffuser of the backlight provides enough back reflection to allow it to be fully sunlight readable without it being truely transflective.
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