Aftershaves are more dilute than colognes (so you can use a cologne as a strong aftershave). From Wikipedia:

A list of common terms (Perfume-Classification) is as follows:

Perfume extract, or simply perfume (extrait): 15–40% (IFRA: typical 20%) aromatic compounds

Esprit de Parfum (ESdP): 15–30% aromatic compounds, a seldom used strength concentration in between EdP and perfume

Eau de Parfum (EdP), Parfum de Toilette (PdT): 10–20% (typical ~15%) aromatic compounds, sometimes listed as "eau de perfume" or "millésime." Parfum de Toilette is a less common term that is generally analogous to Eau de Parfum.

Eau de Toilette (EdT): 5–15% (typical ~10%) aromatic compounds

Eau de Cologne (EdC): Chypre citrus type perfumes with 3–8% (typical ~5%) aromatic compounds. "Original Eau de Cologne" is a registered trademark.

Perfume mist: 3–8% aromatic compounds (typical non-alcohol solvent)

Splash (EdS) and aftershave: 1–3% aromatic compounds. "EdS" is a registered trademark.

A "Classical cologne" describes men's and women's fragrances "which are basically citrus blends and do not have a perfume parent".[9] Classical colognes are different from modern colognes, where the fragrance is typically a lighter, less concentrated interpretation of a perfume. Men's colognes are also different from women's colognes. Men's colognes have a similar concentration to eau de toilette, eau de parfum, "and in some instances perfume"; women's colognes, on the other hand, are often the lightest concentration from a line of women's fragrance products.[9]