A 4-way Valve is a valve which let the fluid pass through 4 different ways. their are different type of 4-ways valves.
A 4-way ball valve have an cross-shaped hole through the middle that's let the fluid goes in one or the other way.
4-way Valves diagram:
A 4-way ball valve have an cross-shaped hole through the middle that's let the fluid goes in one or the other way.
4-way Valves diagram: