Sometimes referred to as open E or open D tuning, Vestapol (or Vastapol/Sebastapol) is perhaps better viewed in terms of the relationship of the strings to the root pitch on the 6th string:
6th string=Root, 5th string=5th, 4th string=Root, 3rd string=3rd, 2nd string=5th, 1st string=Root.
The root, 3rd and 5th are the notes of the major scale that make up the root major chord for whatever key you are playing in: in E, they would be E, G# and B. So if you are tuned to Vestapol in E, playing the open strings will sound an E major chord. The pitches you are tuned to - EBEG#BE - are actually the same as an E chord in standard tuning. If you tune to D, the strings are tuned DADF#AD. Whatever pitch you tune to, the relationship between the strings will always stay the same: R5R35R.
What makes Vestapol convenient as a name for the tuning is the lack of confusion between the actual key the song might sound in and the relationship of the intervals between strings in the tuning. Charley Patton, for instance, plays "Spoonful" in Vestapol at E, or in other words, open E tuning. Furry Lewis plays the slide piece "Falling Down Blues" in Vestapol, but pitched at D, so open D. Josh White plays in Vestapol on songs like Jesus Gonna Make Up My Dyin' Bed, but his guitar is pitched low at C. It's all Vestapol.Not just the name of the place where there is all that aggravation in the Ukraine then. The way that language evolves is strange indeed.