With pedants hat on, this is a not uncommon paragraph for jet operators' manuals:
"Icing Conditions exist when OAT on the ground or TAT in flight is
+10°C or below and visible moisture in
any form is present"
Good enough for me.
Time to raise the other, oft-forgotten rule? If the use of engine anti-ice is anticipated at
any time before the aircraft is clean, it should be included in the RTOW calculations.
I was taught that many years ago and I've always worked to it, but it is amazing how many have never heard of it - or is it wrong.....................?