The temporary economy that starts with each expansion and resets; currency and items there are worth the most early on.
Path of Exile runs leagues of a few months; everything earned migrates to the permanent Standard league at the end. Prices of currency and items in a league fall as it ages, so a listing states the league and the buyer checks how far in it is.
The trade currency the league economy is priced in since the exalted swap; sold per orb.
The permanent league where past leagues' characters and stashes end up; prices there are lower and stable.