Sigla vs. acrónimo
In Spanish, the terms acrónimo and sigla are often confused, but they represent different ways of abbreviating concepts. A sigla is a general term for an abbreviation formed by the initial letters of a phrase, which is usually spelled out and pronounced letter by letter. An acrónimo is a specific type of sigla that is pronounced as a whole, natural word, or it can be a new word created by blending syllables from multiple words.
Sigla
The word sigla translates to initialism. It refers to an abbreviation made from the first letters of the words in a phrase or name, typically requiring the speaker to pronounce each letter individually.
El documento incluye un glosario para cada sigla utilizada en el texto.
(The document includes a glossary for every initialism used in the text.)
A veces es difícil recordar qué significa una sigla tan larga.
(Sometimes it is hard to remember what such a long initialism means.)
El periodista explicó la sigla antes de continuar con la noticia.
(The journalist explained the initialism before continuing with the news.)
Debes escribir el nombre del comité completo la primera vez y luego usar su sigla.
(You must write the full committee name the first time and then use its initialism.)
Nadie en la oficina sabía cómo deletrear la nueva sigla del departamento.
(Nobody in the office knew how to spell the department's new initialism.)
Acrónimo
The word acrónimo translates to acronym. It refers to an abbreviation that is pronounced as a single, phonetic word rather than letter by letter, or a portmanteau created by merging parts of two different words.
El profesor nos pidió inventar un acrónimo para recordar los planetas.
(The teacher asked us to invent an acronym to remember the planets.)
Esa palabra comenzó como un acrónimo pero ahora se usa como sustantivo común.
(That word started out as an acronym but is now used as a common noun.)
El equipo de marketing está buscando un acrónimo pegadizo para el nuevo producto.
(The marketing team is looking for a catchy acronym for the new product.)
Muchas personas no se dan cuenta de que el término es en realidad un acrónimo.
(Many people do not realize that the term is actually an acronym.)
La diferencia ortográfica es importante al escribir un acrónimo en el ensayo.
(The orthographic difference is important when writing an acronym in the essay.)
Summary
To summarize, use sigla when referring to initialisms that are generally read letter by letter. Use acrónimo when referring to abbreviations that can be spoken smoothly as a whole word or created by combining parts of multiple words. While an acrónimo is technically a pronounceable sigla, they function distinctly in Spanish grammar and pronunciation.