MSSI: Multiple Shots, Simultaneous Impact. Sending shots on different trajectories so their travel times differ and they all arrive roughly at the same time at the target (despite being fired one by one).
I once saw a video demonstrating an anti-ship cruise missile (a real life one), they launched four missiles at one target and had them programmed so they moved around the target and struck simultaneously, the missiles were launched in pairs and then circled around the target outside radar range, then turned inwards and struck the target from four different directions. The target’s point defenses were overwhelmed by having to deal with four missiles from different directions at once.
So the idea would be a missile launcher that launches missiles that take different routes so multiple missiles arrive at the same time for harder interception.