What is mutualism?

What is mutualism? Mention any two examples where the organisms involved are commercially exploited in agriculture.

Mutualism is an interaction that confers benefits on both the interacting species. Two examples where organisms involved are commercially exploited in agriculture are:
(i) Mycorrhizae close mutual association between fungi and the roots of higher plants. Fungi help the plant in absorption of nutrients, while the plant provides food for the fungus.
(ii) Lichens represent an intimate mutualistic relationship between a fungus and photo synthesising algae or cyanobacteria. Here, the fungus helps in the absorption of nutrients and provides protection, while algae prepare the food.