Florida law (790.001) says "common pocket knife," not "ordinary."
Porter vs. State, 2001 established that folding knives with blades less 4" are considered common pocket knives. However, knives that have features suggesting they are designed to be used as a weapon, such as serrations, a notched grip, hilt guard, and locking mechanism, could make them run afoul of this even if they are less than 4" (F.R. vs State, 2012). A box cutter or razor knife is definitely considered common (Holley v. State, 2004). Possessing a knife while committing a violent crime, even if the knife isn't used, could make it no longer a common pocket knife (Mims v. State).