Definition - What does Tomentum mean?
Tomentum is also called Trichome, which are the fine appendages or outgrowths on some plants, lichens, algae and protists. They can look like small hairs, scales and/or papillae. The surface in which they grow is called pubescent.
These "hairs" have several functions including absorbing minerals and water, reducing water loss, lowering plant temperature, reflecting sunlight, etc.
WineFrog explains Tomentum
Tomentum are outgrowths which form on the epidermis of various plants, including grape vines. Some are soft to the touch, while others can be prickly.
These hairs may be multicellular or unicellular, unbranched or branched. They can also be glandular and produce a secretion.
Depending on where they are located on a plant, may determine their size, shape and density and thus, their functionality. While they can aid in the physiological aspects of the plant, they can also work as a defense against some pests which might feed on the vine.
They can also keep frost away from the delicate, living cells on the surface of the plant. Another advantage is they help break harsh winds along the plant's surface and can help reduce the negative effects of transpiration.