Fork vertices in the UML Statechart Diagram serve to split an incoming transition into two or more transitions terminating on orthogonal target vertices. The segments outgoing from a fork vertex must not have guards or triggers. Join vertices serve to merge several transitions emanating from source vertices in different orthogonal regions. The transitions entering a join vertex cannot have guards or triggers.
A Fork notation in a UML Activity Diagram is a control node that splits a flow into multiple concurrent flows. This will have one incoming edge and multiple outgoing edges. A join node is a control node that synchronizes multiple flows.This will have multiple incoming edges and one outgoing edge.