Re: what does incisions in a board mean?
esp1 pointed right if the context is about high voltages. When working with high voltages (>1kV) spark gap's (eclators) can be used as cheep protection devices. At an over voltage pulse coming to the spark gap , the electric field between the tracks exceeds a critical level and a breakthrough (spark) occurs in the dielectric (the air) so it can't propagate further on the circuit. The critical level is distance dependent, so the protection level can be adjusted. If you need more explicit info about this just ask