Example

• Subject: Green Fuji Apple
• Category: Agriculture/Fruit

Three Key Words

• No: Green, Fuji, apple
• Yes: Green Fuji Apple, Fuji Apple, Fruit

Apple is a real product, and apple is a kind of fruit, so "apple" and "fruit" can be keywords. Green (color) and Fuji (place of origin or species) are adjectives, meaning they modify "apple". They can not be keywords. Nobody searching with such adjectives will find products.