It's mostly about concentration
The main practical difference between the various fragrance strengths is how much actual perfume oil is dissolved in the alcohol-and-water base. Roughly: Parfum / Extrait is the strongest, typically 20-30%+ oil concentration. Eau de Parfum (EDP) usually sits around 15-20%. Eau de Toilette (EDT) is lighter, typically 5-15%. Eau de Cologne is the lightest, often under 5%. These ranges aren't strict numbers a brand is required to disclose, so treat them as a rough guide rather than an exact promise on any given bottle.
What that actually changes when you wear it
Higher concentration generally means it lasts longer on skin — an EDP will often still be noticeable after six to eight hours, where a lighter EDT might fade within three or four. It also means it projects further (its "sillage" — how far the scent travels off your skin), and often means the scent develops more over the course of wearing it, since there's simply more fragrance oil present to evolve through its top, heart, and base notes.
Which one should you actually buy?
Neither is objectively better — it depends what you want. An EDT can be the right call for a light, everyday scent you don't want announcing itself across a room. An EDP makes more sense if you want a scent to last through a full day or evening without reapplying, or if you specifically loved how a designer original wore and don't want a thinner version of the same idea. The trap to avoid: some cheaper "dupe" fragrances are sold at a low price precisely because they're a much lower concentration than the original they're compared to — meaning you're not really comparing like for like.
Where Voleur sits
Every fragrance in the Voleur collection is blended at genuine Eau de Parfum strength, dosed the way the designer original it's inspired by is dosed — not a lighter, cheaper-to-make version sold to hit a price point.