Definition - What does Head mean?
The head of a grapevine is located at the top of the trunk. This is part of the vine which was originally an individual shoot that was later trained to become the trunk, the main base of the vine that roots into the ground. The head's height is determined by the viticulturist by pruning during its early stages of development.
WineFrog explains Head
The head is an important point in the grapevine. Unlike the arms and canes, which will grow from the head, it will always remain permanent. It is connected to cordons which grow as main branches from the trunk that are trained to grow along a trellis that carry fruit. The height of the head may vary according to trellis systems used, the varietal of grape and desire of the vintner. The trunk and head are part of the main system connected to the roots which provide nutrition, the vine's circulation and water source to the rest of the vine during its lifespan.