Graft union

1. the region where rootstock and scion come together; there can be slightly deformed growth at the union that is noticeable, but does not effect the function of the tree.

The deformity shown in this image is the graft union region on a tree trunk.
Source: https://www.gardeningknowhow.com/ornamental/trees/tgen/what-is-a-graft-collar.htm



This diagram shows a typical grafted plant.
Source: http://www.vnrnursery.in/pop-removal-of-tape-from-graft-union/