Learner's definition of FLOODGATE
a gate for controlling the flow of water from a lake, river, reservoir, etc.
— often used figuratively
Many people fear that the court's latest ruling will open the floodgates for/to a host of new lawsuits. [=will cause/allow a large number of new lawsuits]
Once the floodgates have opened, there will be no way to stop all the lawsuits.