Persillade, pronounced pear-see-yahd is a mixture of chopped parsley and garlic that is added to dishes at the end of the cooking time. It is similar to gremolata, but without the lemon zest.
The word persillade comes from the French word for parsley, persil, and garlic, ail. Usually, to make persillade, and equal amount of garlic and parsley is used. This mixture is widely used in French cuisine.
It features, especially, in Provençal cooking. Sometimes, other herbs such as mint are used in the mixture but still referred to as persillade. Many recipes that list persillade actually use gremolata.
Persillade is frequently used with lamb, where it is spread onto the lamb along with salt, olive oil, etc.
In the video below Mark Bittman makes a dish called Inside-Out Lamb Persillade, which places the persillade, along with olive oil, inside the lamb, to solve the problem of the persillade sliding off during cooking.