Pow means 'prisoner of war'.

[MrsTerryPratchett]

I keep seeing the Princess of Wales referred to as the 'PoW'. It's annoying me so I thought I'd come here and see if anyone else is annoyed.

Didn’t David Cameron think that too? I vaguely remember some email or text exchange that was published where he was attempting to commiserate with a colleague who’d experienced some kind of misfortune, and signed off something like “sorry to hear about your cancer/bereavement/whatever it was, LOL”

Found it:

https://twitter.com/Dannythefink/status/1229779783036342272

I remember that Cameron error. Made a joke about it on Twitter, saying that Cameron also thought that PMSL stood for 'prime minister sends love' and i was retweeted by former deputy prime minister John Prescott. My finest twitter hour

I promise I am not friends with david cameron but that is exactly what my friend did 😬

That is a fine moment.