Often, the terms foul and penalty are used in the same context. For example, you might hear that a player committed a “Pass Interference” foul or penalty.
Here’s the difference, the “Foul” is the act that was indicated by an official which resulted in him throwing his yellow flag. Now, think of the “Penalty” as the punishment for committing the foul.
I’ve always contended that the marker should be referred to as a “Foul Marker” and not a “Penalty Marker.”