The groove starts where there is a significant departure from the plane of the face and this is joined to the side (or wall) of the groove via the edge. The side (or wall) continues to the base of the groove.
The sides (or walls) of the groove must be substantially plain and planar. This disallows features such as bends, indentations in or protrusions from the wall.
The base of the groove must also be substantially plain and join the two opposing sides (or walls) of the groove using a concave shape or a plane.
Groove edges must be a convex curve and must not include serrations, gear teeth or other similar features.
For clubs with lofts less than 25 degrees, where it is difficult to determine whether a groove violates either the edge requirement or the plain wall requirement, the groove will be deemed to meet the plain wall requirement.
Based on all of the above, the following images are illustrative examples of permissible groove geometries: