Maybe "fraction" would be suitable.

I use "andel", but if you don't write your variable names in Danish, then it might look a little strange. "Share" would be the direct translation, but that word usually means something else in programming. In English, I use "ratio" also; in context the meaning is always clear enough.

From one perspective it is the "normalized" unit, so not giving it a name makes as much sense as trying to find a word for it: if you were going to call something ProgressPercent the normalized float/double form is just Progress. This is probably the closest to what I try to stick too, but it can be hard especially if you have six other things that also want to be called "Progress" that aren't normalized floats/doubles.

(Another name for the "normalized" unit is sometimes the "unit" unit. ProgressUnit sounds dumb, but is an available option in English and shorter than ProgressNormalized.)

Not GP, but 0.5% == 0.005, not 0.5.

Suppose our application deals with classifying cheese, and has a field for how much fat a given sample has, maybe it needs 20% to be classified as Grade A Ste-Madeleine-de-la-Foo. Some developers like to call this field MinimumFatContentPercent and set it to 0.2.