Does anyone know if there is a term for the letters that are dropped in an acronym? Any reply would be greatly appreciated.

I would be surprised if there is a word. I am happy to be corrected though. Can you give an example?

Please excuse my question, but do you mean an acronym? As you probably know, an acronym is an abbreviation spoken like a word. So, "BBC" is not an acronym but "UNICEF" is. Often in abbreviations, only the principal words are represented. Words like "of", "a", etc. are often ignored. Is this what you mean?