Okay kiddo, so you know how oranges are yummy and they have that citrusy smell? Well, petitgrain is actually made from the leaves and twigs of orange trees!
So sometimes, people don't just want to eat oranges, they also want to smell like them or use their scent to make things smell nice. That's where petitgrain comes in. People take the leaves and twigs and steam them to get the special oils out. Those oils are then used to make perfumes, soaps, and other things that smell good.
It's kind of like making tea - you put the leaves in hot water and let it steep. But instead of drinking it, you take the oils and use them to make things smell good! And the best part is, it's all natural and comes from the orange tree, just like the yummy oranges we love to eat :)