Chiffonade is a cooking technique in which herbs or leafy green vegetables (such as spinach and basil) are cut into long, thin strips. This is generally accomplished by stacking leaves, rolling them tightly, then cutting across the rolled leaves with a sharp knife, producing fine ribbons.
To chiffonade, place a large stack of basil leaves in your fingertips, largest leaves at the bottom. Roll tightly and place down on a cutting board and cut thinly across, while keeping your knife tip in contact with the board at all times.
The term comes from the French language. It means "made of rags" referring to the fabric-like strips that result in this technique.