What do you call an abbreviation consisting of the first letters words pronounced separately?

There isn't a specific, universally recognized term for an abbreviation consisting of the first letters of words pronounced separately.

However, you can use various terms depending on the context and the type of abbreviation:

General terms:

* Initialism: This is the most common and general term for such abbreviations, even though it's often used interchangeably with "acronym." Examples: FBI, USA, NATO.

* Letter abbreviation: This is a more descriptive term that emphasizes the use of letters.

More specific terms:

* Acronym (with caveats): Technically, an acronym is pronounced as a word (like "NASA" or "SCUBA"). However, many people use "acronym" even for initialisms that are pronounced letter by letter.

* Alphabetic abbreviation: This term emphasizes the alphabetical sequence of the letters used.

* Letter code: This term is suitable for abbreviations that function as codes, like "RSVP" for "Répondez s'il vous plaît".

Examples:

* FBI: Initialism, letter abbreviation, alphabetic abbreviation

* USA: Initialism, letter abbreviation, alphabetic abbreviation

* RSVP: Initialism, letter abbreviation, letter code

Ultimately, the best term to use depends on the specific context and your intended meaning.