Step 1: Understanding forage preservation.
Green fodder is preserved for cattle through drying or fermentation: - Drying fodder results in Hay. - Fermentation under anaerobic conditions produces Silage.
Step 2: Analyze the options.
- Hay: This is dried grass, not a fermented product.
- Green manure: Crops cultivated for incorporation into the soil, not for fodder preservation.
- Silage: Fermented green fodder stored in pits or silos, designed to retain nutrients for cattle.
- Green cakes: These are oil cakes, utilized as cattle feed but not a form of fermented forage.
Step 3: Conclusion.
Therefore, silage is the name given to the fermented product of green forage.
Final Answer: \[\boxed{\text{Silage is the fermented product of green forage.}}\]