Why IARP stands for International Amateur Radio Permit, created by the Inter-American Convention on an International Amateur Radio Permit (CITEL). It lets a licensed US amateur operate in other signatory countries of the Americas without applying for a separate reciprocal license from each one. In the US the permit is issued by the ARRL as the FCC-recognized issuing organization, and it is the Western Hemisphere counterpart to CEPT operating privileges in Europe.
Watch out The choices about reflected power and aurora forecasts are just plausible-sounding radio jargon built from the letters; IARP is purely a licensing document, not a measurement or propagation term.
IARP = International Amateur Radio Permit: your passport to operate in the Americas. CEPT for Europe, IARP for the Americas.