The verb “to forage” means to hunt for food or to collect food. So bees that are foraging are collecting food and are referred to as foragers.
The noun “forage” refers to the food itself. Forage for bees comprises both pollen and nectar, but you could also include water since bees have to go and find it and bring it home. Foraging range refers to the distance bees can or will travel in order to find food or water.
Forage often refers to natural food sources found in the environment, although bees collect food from both wild and cultivated plants. Forage for livestock, on the other hand, is usually planted specifically for them. A field of clover or alfalfa can provide forage for both cattle and bees—as well as for unwanted creatures such as alfalfa weevils and leaf hoppers.