Salsa verde means "green sauce" in Italian, and is a flavorful, green herb sauce. In addition to lots of parsley and preferably fresh basil, the sauce is made with garlic, mustard, white wine vinegar, capers, possibly anchovies, and good olive oil. The sauce is blended in a food processor and served cold.
Visually, Salsa verde can resemble Pesto alla genovese, which is also green, but the flavors are completely different. Classic pesto is based on basil and contains parmesan and nuts, which are not found in Salsa verde, while Salsa verde is based on parsley and has a somewhat salty and tangy umami flavor from capers, mustard, and anchovies.
Throughout Italy, you can find slightly different variations of salsa verde. Salsa verde toscana from the region of Tuscany often contains a hard-boiled egg that is mashed into the sauce, while the sauce is made with both hard-boiled egg yolk and a bit of bread in Piedmont (Salsa verde piemontese or Bagnetto verde).
Salsa verde also means "green sauce" in Spanish, and the Italian sauce you have a recipe for here should not be confused with Mexican Salsa verde. Mexican Salsa verde is much spicier and made with green tomatillos (which look like small green tomatoes), fresh cilantro, parsley, onion, garlic, lime, and jalapeños (green chili).
Check out the recipe for Chimichurri, which is a popular herb sauce from Argentina, made with fresh oregano, flat-leaf parsley, garlic, chili, red wine vinegar, and olive oil.
Italian Salsa verde is made without chili and is mild, but still full of flavor! Especially delightful as a side for grilled meat, chicken, fish, and boiled eggs. Salsa verde is also served with roasted potatoes, vegetables, and as a dressing on salads. For example, see Tomato salad with mozzarella and salsa verde.