UPnP allows devices to open up firewall ports for themselves to allow traffic to reach them inbound. Games (for example) that that host a server on the users lo

UPnP allows devices to open up firewall ports for themselves to allow traffic to reach them inbound. Games (for example) that that host a server on the users local machine may require an open port to allow access inbound so UPnP can help with this. Now-a-days it's not used much and quite frankly it was always a fairly bad idea.