Learn English – Is IOU an abbreviation, an acronym, or an initialism

If you look at the third definition of acronym, it directly addresses your question. BBC is an acronym, regardless of whether it is pronounced as letters or as a word. RAM (random access memory) is an acronym whether it is pronounced ram or are-aye-em.

SUPPLEMENT

There is a controversy as to whether initialisms are a subset of acronyms or a distinct class of terms.

Several dictionaries seem to restrict acronyms to those shortened forms that can be pronounced as a word. See, e.g., Oxford Online, Collins, and American Heritage.

Others include initialisms as a form of acronym. See, e.g., the OED, Merriam-Webster and Websters New World. Wikipedia has an article on acrnoyms which notes a difference of opinion as to whether initialisms should be included, and then proceeds within the article to include them. It also notes that there are a number of forms that do not neatly fit into either category, such as JPEG (pronounced jay-peg) and AAA (usually pronounced Triple A).

There is also the interesting evolution of an acronym found in the abbreviation for Standard Oil. It began with SO, a clear initialism, which them morphed to ESSO, a classic acronym. (The company has since become EXXON which does not seem to stand for anthing.

Yes, sitcom can be considered an acronym.

The ODO definition is a bit too restrictive, if you ask me.

Compare it to the OED, which has two distinct senses of the word: the first is identical to initialism (i.e., when each letter in the acronym is pronounced individually); the second is:

A word formed from the initial letters of other words or (occas.) from the initial parts of syllables taken from other words, the whole being pronounced as a single word (such as NATO, RADA). [My emphasis]

The Merriam-Webster definition is also more inclusive:

a word (as NATO, radar, or laser) formed from the initial letter or letters of each of the successive parts or major parts of a compound term

Both these definitions tally with the very first two sentences in the Wikipedia article on acronyms:

An acronym is an abbreviation formed from the initial components in a phrase or a word. These components may be individual letters (as in laser) or parts of words (as in Benelux and Ameslan).

All this does not mean that ‘acronym’ is the first thing people think of when they hear sitcom—it is an option, but I would not call it the ideal description. Sitcom is a more typical case of blending, so if you are simply looking for a word to describe sitcom (rather than specifically wondering whether you can describe it as an acronym), I would use that instead.