A pinafore, like the green and white check one I'm wearing here, (which I got in the Urban Outfitters sale. Similar here) is actually an apron, according to Wikipedia. And it's supposed to be "protective". In America they're actually called jumper dresses (is that correct American friends?!) This is already far too confusing.
Meanwhile the dungaree, or overall, or over all, or overalls, or bib-and-brace overalls, or party bibs - my new favourite name for them - are also supposed to be something you wear to shield the clothing underneath. Ideal for people who do work that might mess up their nice white shirts, or are like me and find chocolate marks all over their tops. Even when I haven't eaten any chocolate. Since the 1960s cool people of the world have worn them to be cool because that is what cool people do. Some of my favourite overall/dungaree wearers in pop culture are listed below.
1. Lake Bell's character Donna in Wet Hot American Summer: First Day Of Camp
2. Sasha Jenson's character Don (wait, Don, Donna?!) in Dazed And Confused
3. Heather O'Rouke as Carol in Poltergeist
4. Larisa Oleynik as Alex in The Secret World Of Alex Mack
By the way if you have Netflix I recommend the behind the scenes mini doc made when they filmed the original Wet Hot American Summer in 2001. It's called Hurricane of Fun: The Making of Wet Hot and is worth it if only to see a youthful Bradley Cooper talking about the role - his first out of acting school.