I is Interlaced, meaning it goes from top to bottom skipping every 2nd line and then goes a 2nd time doing the skipped lines next
P is progressive meaning it goes top to bottom once and does every line.
So Interlaced gives you half the picture and then the other half and Progressive takes a bit longer to give you the whole picture. Because of the speeds and persistence of vision either way will create motion out of it. I'm not sure how many people would see any difference.