This is a terminology question. Technically multi-hit moves use multiple hits, and OKHO is defined as 1 hit by its direct translation. However, when anyone talks about OHKO (or 2/3/4/X- HKO) in Pokemkon, the meaning is X amount of turn(s) are used. So, can I call a multi-hit move an OHKO if it hits at least twice and KOs the foe after only the first turn of battle?
For example, Octillery enters battle and uses Rock Blast on a full health Pidgeot. Rock Blast hits 3 times and KOs Pidgeot in one turn. Did Octillery OHKO Pidgeot?
Yes, this does have a practical application: XHKO calculations are often used in planning stats and movesets of Pokemon. It would be confusing if I couldn't call Octillery's Rock Blast on Pidgeot an OHKO, but it would also be confusing if I could because it technically is more than one hit.... Anyway, which way is it so I know what terminology to use in my battle calcs?