From the Super Mario Wiki, the Mario encyclopedia
Climbing Grass is a type of helpful vegetation found in Donkey Kong Country Returns / 3D and Donkey Kong Country: Tropical Freeze. It is grown along various surfaces, such as platforms, walls, and ceilings, and can be grasped and climbed in the same manner as vines to escalate said surfaces. This can help cross dangerous pits and other obstacles, or access higher grounds and rooms. Climbing Grass may also lead to secret areas concealing items such as Puzzle Pieces, though most of the time these paths are obscured by foreground elements, like leaves.
Before Climbing Grass was changed to resemble ivy in Donkey Kong Country: Tropical Freeze, it appeared as generic grass in Donkey Kong Country Returns. It was referred to as green surface or, more particularly, green grass, as Donkey Kong Country Returns presents other climbable formations, green chains, which are wrapped on various surfaces across the Factory. Stompybot 3000, the boss of this area, reveals a patch of green chains underneath it, which can be clung to and then pounded to inflict damage on the enemy.