What is the difference between an acronym and an initialism?

In my last employment at NHSU (the ‘university’ for health and social care, now defunct), I came across many many abbreviations. The public sector is particularly riddled with such shortenings, for committees, programmes, policies and what have you. For instance, from the health/learning sector, IAG: Information, Advice and Guidance, KSF: Knowledge and Skills Framework; the Department of Health itself is the DH not, unfortunately, DoH. These are known as TLA (three-letter acronyms).

Yet these kind of abbreviations are not acronyms but initialisms.

Acronym n. A word formed from or based on the initial letters or syllables or other words.

The main point is that the initials have to form a pronouncable word, as in Scuba – self-contained underwater breathing apparatus – and radar – radio detection and ranging. So modern abbreviations inspired by restricted character limits in text and Twitter – LMAO: Laughed My Arse Off, IMHO: In My Humble Opinion and HNY: Happy New Year, a new one I discovered a few weeks ago – aren’t acronyms but initialisms.

But abbreviating sentiments to initials is nothing new. Here’s a good acronym I found in my research (from businessballs.com):

CHIP: Come Home I’m Pregnant
An acronym gem from the Second World War, and potentially applicable today for husbands on prolonged residential training courses, drilling rigs and overseas work assignments – see also ITALY, HOLLAND, SWALK, BURMA, EGYPT and NORWICH.