Definition - What does Tendril mean?
A tendril is a thread-like structure that grows from the node to support climbing plants. It is a slender structure, which can coil around small objects in the vicinity of the plant and support the weak stem. Grape vines, like all vines, are climbers and depend on their tendrils for support and growth.
WineFrog explains Tendril
A tendril might be a variation of both stem and leaf. It is mostly found opposite a leaf at the node, and the adhesive pads present in a tendril enable it to hold strongly to any object that it can wrap around. Some parasitic plants also use tendrils to invade other plants.
Grapevines have a very weak stems and cannot stand straight upright on their own without the support of tendrils. So, they require their tendrils to coil around sticks, other plants or similar objects to maintain a vertical position. Correct posture is very important for the grapevines in order to continue their growth. Tendrils, like leaves, can also participate in photosynthesis and help plants to obtain vital nutrients. Additionally, tendrils can also be used in the production of brisk wine.