What do aphids produce that attracts ants?

Aphids produce honeydew, a sugary substance that is excreted as a byproduct of their feeding on plant sap. Ants are attracted to this sweet substance because it serves as a food source for them. In many ecosystems, a mutualistic relationship exists between ants and aphids; ants will protect aphids from predators in exchange for access to the honeydew. This relationship benefits both species, as ants receive nourishment while aphids gain a level of safety from their natural enemies.

While nectar, which is produced by flowers, is also sweet and can attract ants, it is not produced by aphids. Pollen serves as a food source for many insects, including some ants, but aphids do not produce pollen either. Waste could refer to the excretion of various substances, but in the context of aphids, it is specifically the honeydew that holds significance and attracts ants.