A unit of measure, not too precise. It's as far as you can stretch your thumb and middle finger away from each other. Nobody uses it for any measurement that needs to be written down, everybody uses metric here, it's just a handy expression in real-life situations.
The only time I remember pedalj being in practical use is when we were playing marbles as kids. Then the distance between the hole and starting line was 8 pedalja or something (maybe 10 for big hole and 7 for small?)(nope, that was measured in hand's breadths).