3P4W stands for Three Phase and Four Wires. It is "STAR" type connection which is used to connect various switchgear equipment.

3P3W stands for Three Phase Three Wire. It is basically regarded as "DELTA" type connection used connection.

(1) In STAR type configuration, either the starting points of phase wires or finishing ends of the phase wires are connected together in order to shape the neutral point. There’s no such connection in Delta type configuration.
(2) Star configuration is used when phase voltage is required.
(3) In star type configuration VLine = √3 VPhase. Where as Line Current equals to Phase Current
(4) The Star type configuration is preferred more over Delta type in Transmission systems due to less insulation is required in Star type than to that of Delta type configuration.
(5) In Delta type configuration, VLine equals to Vphase whereas, the line current is equal to root 3 time the phase current in Delta type configuration.