Intrusion detection is a security process that monitors a network or system for suspicious activities or violations of policies. It helps identify potential threats, such as unauthorized access or attacks, by analyzing data and user behavior. There are two main types of intrusion detection systems: network-based and host-based. Network-based systems monitor traffic across the entire network, while host-based systems focus on individual devices. Both types aim to alert administrators about potential security breaches, allowing for timely responses to protect sensitive information.