Parboil

Par boiling is to part boil food. If you like, to soften up the food ahead of the main cooking process.

Potatoes

I find the easiest test of a parboiled potato is to stick a fork into two or three of the chunks. If the fork goes in with ease then they are ready. If some are soft and others still hard then you haven’t stirred the potatoes frequently enough. If the fork goes straight through cutting the chunk in half then you’ve over boiled them and they will likely disintegrate to mush.