collard greens means: A variety of greens that have a hardy leaf and a sharp taste, somewhere between cabbage and kale or turnip and other members of the mustard family. They can vary in their sweetness and mildness depending on how old they are. The stalks of too hard to consume Collards are not enough for them to form heads. (in Cooking Dictionary)

What else does collard greens mean?

This leafy dark green vegetable has paddle-shaped leaves and grows on tough, tall stalks. It tastes similar to cabbage or kale. (in Cooking Dictionary)