IDS stands for Intrusion Detection System. An Intrusion detection system is a software application that monitors for viruses, hacking, or breaching on a certain network or system.
You can install an Intrusion detection system to keep your network safe as well as a firewall. Whenever people make a new software and they are in the process of making it they install an IDS on it so while they are making it nothing breaches it while it is still vulnerable.