the.com/purchasing power

means The real amount of goods or services a given sum of money can buy, which shrinks as prices rise even if the number in your account stays the same.

from A straightforward economic compound, pairing 'purchasing' (from Old French 'porchacier' — to pursue or go after, originally hunting language, later softened into the act of buying) with 'power' in its old sense of capacity or ability. The phrase itself is a product of modern economic thought, emerging as economists needed a precise way to separate the face value of money from what it could actually command in the marketplace — especially once inflation made those two things visibly diverge.