Definition - What does Primary Bud mean?
The primary bud on the grapevine is the most likely part to develop a robust fruiting shoot during the growing season. It is centrally located in the dormant/compound bud on the vine and is the largest out of the three buds (primary, secondary or tertiary).
The primary bud is the first to grow after the winter dormant period and develops into stems and leaves that give way to flowers and berries.
WineFrog explains Primary Bud
Each spring, the dormant bud starts to develop its largest or primary bud that will cultivate during the growing season. This primary bud is the largest and most noticeable compared to the secondary and tertiary buds. It is the most important and will produce the highest crop yields compared to the other buds.
If there is an injury to the primary bud that causes it to die, the secondary and tertiary buds will grow shoots, leaves and fruit, but, it will not be as strong or as plentiful as it would have been from the primary bud.