Definition - What does Graft mean?
In botany, a graft plant occurs when one plant is grafted to another. The host plant supports the graft, which then grows as it would if it were still attached to the original plant. Many plants can be grafted successfully, with potatoes/tomatoes being one of the most popular.
The process of creating a graft is not particularly difficult, and has been practiced for thousands of years. A stem is cut from the donor plant and is chosen based on particular criteria (thickness, the presence of buds, flowering potential, and more). Then, a slit is made in the bark/skin of the host plant. The stem is then inserted into the slit.
MaximumYield explains Graft
A graft is essentially a piece of one plant surgically added to another. For instance, grape varietals are often grafted onto different root stock to provide protection from diseases or in-soil threats like fungi that one species might be adapted to, but the desired crop is not. Tomatoes can be grafted onto potato plants to create a more productive garden plot. There are many other examples of grafting at work, as well.
It can take many weeks for the graft to show signs of growth, and such grafting can only be truly successful if the grower manages to put the vascular tissues of the stem and the rootstock in contact with one another.
As a word of caution, the joint formed by grafting a stem onto rootstock is never as strong as a standard joint, and can create a weak point in the plant, allowing damage, or even disease to affect it.
Note that in a graft, only the vascular tissues and bark/skin of the plant fuse. Woody tissue does not (a primary cause of joint weakness).
Note that grafting is separate from tissue culture. In tissue culture, which is also done in a lab, plant tissue is taken from one plant and allowed to grow into a duplicate of the host plant. Tissue culture is a form of cloning, whereas grafting creates new types of plants altogether.