What does it mean to have an incomplete right bundle branch block?

Not much: It is a benign EKG finding related to a slight delay in the conduction system (like electrical wiring) of the heart. It is more common in those with an atrial septal defect (hole between left and right heart) but in general is benign, nothing to worry about.

Very little: While this can be a manifestation of some mild abnormalities like asd, the vast majority of incomplete right bundle branch block is a normal variant finding. If all else is well with your heart and an echocardiogram confirms normal structure, you're good to go. Many would argue that even the echo is unnecessary if the clinical exam (with a stethoscope) is entirely normal.