Rectified spirit
Also known as: 95% spirit, neutral spirit, Everclear, spirytus rektyfikowany
Ethanol run through rectification up to 95–96%. The rest is water, and distillation cannot remove it because the azeotrope gets in the way.
Rectification throws out more than water. Out go the higher alcohols, aldehydes and esters — everything that gives a distillate character. Rectified spirit is meant to be neutral: to smell and taste of nothing but alcohol. Which makes it a good base for a liqueur whose flavour should come from cherries or honey, not from the spirit itself.
Whisky, cognac and rum deliberately go the other way: they are distilled to a lower strength precisely so that some of those compounds survive.
Not to be confused with denatured alcohol. That is also ethanol, but deliberately contaminated, and the denaturants cannot be removed at home.
In practice: to bring 95% spirit down to 40% vodka you add roughly 1.375 litres of water per litre of spirit. For other strengths the calculator will work it out, along with the real volume after contraction.