Intrusion Detection Systems (IDS) analyses network traffic for signatures that match known cyber attacks. Intrusion Prevention Systems (IPS) also analyses packets, but can also stop the packet from being delivered based on what kind of attacks it detects — helping stop the attack.
Intrusion Detection Systems (IDS):analyses and monitor network traffic for signs that indicate attackers are using a known cyber threat to infiltrate or steal data from your network. IDS systems compare the current network activity to a known threat database to detect several kinds of behaviors like security policy violations, malware, and port scanners.
Intrusion Prevention Systems (IPS):live in the same area of the network as a firewall, between the outside world and the internal network. IPS proactively deny network traffic based on a security profile if that packet represents a known security threat.