Originally Posted by AngelicaDeAlquezar (Post 51802)

Adding to Sosia's explanation:

In Spanish, all abbreviations (abreviaciones) in plural must have their letters written twice:

EEUU = Estados Unidos
FFCC = Ferrocarriles
DDHH = Derechos Humanos


"Siglas" are different. They're formed by taking the first letter of each word:

EUA = Estados Unidos de América
ONU = Organización de las Naciones Unidas
FMI = Fondo Monetario Internacional


An "acrónimo" is formed taking several letters from the title to make words one can pronounce:

Conagua: Comisión Nacional del Agua
Semarnat: Secretaría de Medio Ambiente y Recursos Naturales
Ferronales: Ferrocarriles Nacionales