The same formula. Three different strengths. The difference determines whether your perfume reaches Act 3 or disappears before lunch.
Perfume concentration refers to the percentage of aromatic compound — the fragrance oil — dissolved in the alcohol-water carrier.
Extrait de parfum (pure parfum): 20–40% fragrance oil. The most intense, longest-lasting, most expensive form.
Eau de parfum (EDP): 15–18% — the standard for fine fragrance. Projects well, lasts 6–12 hours on most skin.
Eau de toilette (EDT): 4–8% — lighter, shorter-lasting, typically 3–5 hours.
Eau de cologne: 3–5% — highly citrus-forward, 2–4 hours maximum. All edpclub releases are EDP concentration. This is not a compromise. It is a structural decision.

DIFFERENCE
Imagine perfume as a drink. The "perfume oil" is like the flavoring, and the "alcohol" or "alcohol-water mix" is the liquid it's mixed in.
- Eau de Parfum (EDP) is a strong drink. It has a good amount of flavoring (15-18% perfume oil) in mostly alcohol (80-90%). Because it's strong, the scent lasts a long time.
- Eau de Cologne is a weaker drink. It has less flavoring (3-5% perfume oil) and is mixed with a lot of alcohol and some water (70% alcohol-water mix). The scent won't last as long as an EDP.
Historically, "cologne," "toilet water," and "parfum" started as names for scents from different places or cultures. Only later did they become official terms for how concentrated a scent was (like strong, medium, or weak).
The science behind it is that special ingredients in the stronger perfumes (like EDP) are like "slow-down" molecules. They make the scent evaporate more slowly, so you can smell it for longer. This slow-down effect really works best in the stronger concentrations, like Eau de Parfum and above.

TAKEAWAY
Buy EDP for balanced performance — strong enough to project, stable enough to reach Act 3.
If you want maximum longevity and intensity, extrait.
If you want something light for daytime or office wear, EDT.
Concentration is structural. It tells you what the formula can and cannot do before you open the bottle.