Agave nectar, also called agave syrup, is a liquid sweetener made by extracting, filtering, and heat-concentrating the sap from the core of agave plants, primarily blue agave grown in Jalisco and other Mexican states. "Nectar" is the more common name in the U.S.; "syrup" is used elsewhere, but the two names describe the same product.
Producers harvest the plant's core (the piña), press out the sap, then filter and heat it to the desired thickness. Lightly processed nectar has a mild, neutral sweetness; darker, longer-processed versions take on caramel- and molasses-like notes. It dissolves easily in hot or cold liquids and is commonly used in place of honey, maple syrup, or granulated sugar in baked goods, beverages, marinades, and dressings; it pairs well with citrus, spices, and chili.
Agave sap itself has been harvested by indigenous Mexican cultures for centuries for drinks such as pulque. Agave nectar as a bottled commercial sweetener, by contrast, is a modern product that took off from the late 20th century onward.